explain xkcd - User contributions [en]

Talk:3076: The Roads Both Taken

2025-04-17T15:03:47Z

172.70.91.129:

I just saw on Google's Doodle: "''...today’s Doodle shows an illustration of quantum superposition. April 14 is World Quantum Day, and this year is also the International Year of Quantum — celebrating 100 years since the discovery of quantum mechanics.''" https://blog.google/technology/research/world-quantum-day-doodle-superposition-thaumatrope/ --[[User:PRR|PRR]] ([[User talk:PRR|talk]]) 05:25, 15 April 2025 (UTC)
:Added World Quantum Day to the article. Thanks. [[User:Nitpicking|Nitpicking]] ([[User talk:Nitpicking|talk]]) 13:25, 15 April 2025 (UTC)

I think "Photon poetry" is a reference to Vogon poetry in Hitchhiker's Guide to the Galaxy (notoriously the worst poetry in the universe). [[Special:Contributions/104.23.172.2|104.23.172.2]] 07:19, 15 April 2025 (UTC)
:Actually, vogon poetry is 3rd worst, but I see your point and shared the same thought process. I think this should be added into the article. {{unsigned ip|172.68.84.192|05:21, 16 April 2025}}

Pretty sure the title text is a parody of a song lyric that I can't remember the original of. "When you something something something, that's something". Damn it, its on the tip of my tongue, but it isn't quite coalescing! {{unsigned ip|162.158.110.237|09:56, 15 April 2025 (UTC)}}
: When a grid's misaligned with another behind, that's a moiré! [[Special:Contributions/172.70.160.217|172.70.160.217]] 10:06, 15 April 2025 (UTC)]
::When the spacing is tight
::and the difference is slight,
::That's a moiré. [[User:DollarStoreBa'al|DollarStoreBa'al]] ([[User talk:DollarStoreBa'al|talk]]) 13:56, 15 April 2025 (UTC)
: I think it's more likely a slightly clunky way to reach the punchline that is a twist on photon-superposition-fomo being ''phomo'' [[User:Xseo|Xseo]] ([[User talk:Xseo|talk]]) 10:15, 15 April 2025 (UTC)
: The original was {{w|That%27s_Amore|a hit for Dean Martin in 1953}}. [https://arnoldzwicky.org/2015/10/17/thats-a-moray/ Parodies featuring moray eels came later]. I agree with Xseo that Martin's song is unlikely to have been an inspiration for the title text. [[Special:Contributions/108.162.246.82|108.162.246.82]] 14:40, 15 April 2025 (UTC)
:: My favorite is: When you make béchamel and throw cheese in as well that's a Mornay.[[Special:Contributions/172.69.246.135|172.69.246.135]] 01:59, 16 April 2025 (UTC)
:::When it causes a stir in your social milieu, that's a more. [[Special:Contributions/172.71.241.100|172.71.241.100]] 13:51, 16 April 2025 (UTC)
::::When the eel's teeth are like saws,
::::And on two pairs of jaws,
::::That's a Moray... [[Special:Contributions/172.70.91.129|172.70.91.129]] 15:03, 17 April 2025 (UTC)

Two roads diverged in a wood, and I— 
I took the one less traveled by, 
And I'm beginning to see why. [[Special:Contributions/172.69.180.164|172.69.180.164]] 19:43, 15 April 2025 (UTC)
:funny you should say that. from Wikipedia, {{quote|After Frost returned to New Hampshire in 1915, he sent Thomas an advance copy of "The Road Not Taken". Thomas took the poem seriously and personally, and it may have been significant in his decision to enlist in World War I. Thomas was killed two years later in the Battle of Arras.}} [[user talk:lett‪herebedarklight|youtu.be/miLcaqq2Zpk]] 06:48, 16 April 2025 (UTC)

Talk:3067: SawStart

2025-03-25T10:20:00Z

172.70.91.129:

It's weird seeing a totally empty explanation, also whats the point of sawstop, don't they just use vibrating blades? [[Special:Contributions/104.23.190.110|104.23.190.110]] 12:40, 24 March 2025 (UTC)
:SawStop is for rotating blades, like you would use for sawing wood. I'm sure there's a good reason why they don't use vibrating blades there, the most likely is "wood is harder than a plaster cast". I could also imagine that vibrating blades don't create nice cuts, which doesn't matter with a plaster cast that will be disposed of, but very much matters with wood used for construction. --[[User:Coconut Galaxy|Coconut Galaxy]] ([[User talk:Coconut Galaxy|talk]]) 13:16, 24 March 2025 (UTC)

empty explanation is freaky woah [[Special:Contributions/172.69.194.204|172.69.194.204]] 12:42, 24 March 2025 (UTC)
:Every explanation is empty, at least for a short amount of time. And this is not the earliest that a comic went up (shortly after midday, UK time, when it's not unknown for them to not arrive until after the midnight at the end of the designated publication day), but it looks like you (both, including first-poster at the top) have had the good luck/fortune to be just casually checking for new changes to old articles on the site and instead get 'first look' at the newest addition to it. Of course, it'll be a few hours before most of the article gets fine-tuned into some form of 'completion'. [[Special:Contributions/172.70.86.157|172.70.86.157]] 13:23, 24 March 2025 (UTC)
sudo systemctl stop saw-start.service [[Special:Contributions/172.69.208.132|172.69.208.132]] 13:11, 24 March 2025 (UTC)
:yay you saved the world! --[[User:Bb777|hi]] ([[User talk:Bb777|talk]]) 14:08, 24 March 2025 (UTC)
:"Failed to stop saw-start.service: Access restricted by systemd security policies"
:sudo holding-in-the-power-button doesn't work either.[[Special:Contributions/172.69.34.139|172.69.34.139]] 17:26, 24 March 2025 (UTC)

I'm 99% sure that the system is designed to start a ''stopped'' blade up to full speed within milliseconds, not just increase the speed of a spinning blade. --[[User:Coconut Galaxy|Coconut Galaxy]] ([[User talk:Coconut Galaxy|talk]]) 13:22, 24 March 2025 (UTC)

WAITER, WAITER, MORE [[Black Hat]] PLEASE [[User:CalibansCreations|'''Caliban''']] ([[User talk:CalibansCreations|talk]]) 13:31, 24 March 2025 (UTC)

Because of gyroscopic precession, a still spinning (unstoppable?) blade, removed from its axle and housing, would be /very/ difficult and dangerous to dispose of. I'm a woodworker and I think I'll be having nightmares tonight.
-DW [[Special:Contributions/172.69.23.176|172.69.23.176]] 13:36, 24 March 2025 (UTC)
: At least if it's unstoppable we can use it as a free source of energy! [[Special:Contributions/172.69.195.62|172.69.195.62]] 14:01, 24 March 2025 (UTC)

As a woodworker, one note I would like to make is that while the sawblade ''can'' be damaged by cartridge activation, it is not ''required'' that it be replaced. It is possible to have the blade inspected and potentially repaired and continue to use it. That is addressed in SawStop's FAQ https://www.sawstop.com/sawstop_faq/can-the-blade-be-reused-if-the-safety-system-brake-is-activated/ [[Special:Contributions/172.69.33.189|172.69.33.189]] 15:04, 24 March 2025 (UTC)

The [citation needed] for violating other laws probably means that law enforcement should issue a citation to the manufacturer. [[User:Barmar|Barmar]] ([[User talk:Barmar|talk]]) 15:21, 24 March 2025 (UTC)

General observation from a s/w test engineer/woodworker: Original version of the Sawstop used a shotgun shell to fire a stopper into the sawblade which absolutely did destroy the blade. (and made enough noise to pretty much ensure a 'code brown' if you triggered the stop system.) Newer version uses a high tension spring along with a deformable aluminum stopper assembly to absorb the energy and bring the blade to a stop. The advantage of the deformable aluminum assembly is that you can remove it from the blade (with care) and as noted can put the sawblade back to work. However you need a new ($200-ish) stopper assembly before you can re-start the saw. Having a family member who is a retired emergency room doctor who would regularly email me 'stories from work' of woodworker injuries who came through her ER, I can assure you that a tablesaw is pretty much the most dangerous woodworking tool in a typical woodshop. That being said, its quite amusing to me that "SawStop" became XKCD worthy. SawStop is somewhat notorious in the woodworking community because of their highly obnoxious business practices with regards patent and legal attacks on business competitors who came up with alternative approaches to the 'saw brake' or 'saw safety' system. JC from Canada {{unsigned ip|172.69.33.194}}

Funnily enough this could be practical in robot combat [[Special:Contributions/104.23.190.15|104.23.190.15]]15:01, 24 March 2025 EST

Note that since the blade is spun up using explosives and not the electric motor (even ignoring the title text), the saw being unplugged in no way makes the blade safe to touch. [[Special:Contributions/172.68.23.226|172.68.23.226]] 20:03, 24 March 2025 (UTC)

The explosive charge whould already be deadly. --[[User:Bb777|[insert signature here]]] ([[User talk:Bb777|talk]]) 00:31, 25 March 2025 (UTC)

Why is it important to include the fact that this could be used in robot warfare? [[User:Ozymandias|Ozymandias]] ([[User talk:Ozymandias|talk]])

3065: Square Units

2025-03-20T13:55:10Z

172.70.91.129: /* Table of conversions */ Suggestion.

{{comic
| number = 3065
| date = March 19, 2025
| title = Square Units
| image = square_units_2x.png
| imagesize = 545x678px
| noexpand = true
| titletext = The biggest I've seen in a published source in the wild is an 80-fold error in a reported distance, which I think came from a series of at least three unit conversions and area/length misinterpretations.
}}

==Explanation==
{{incomplete|Created by a BUG IN A SQUARE AREA DEFOLIATION BOT - Do NOT delete this tag too soon.}}

In this comic, [[Megan]] is using her phone to read about an insect species that consumes (hyperbolically described as 'devours') one square inch of grass per day. As it is relayed through a chain of conversations, this measurement gets misinterpreted 11 times until [[Hairbun]] tells other people that it devours an area of grass equal to two times the land area of Australia per day, which is clearly impossible by one insect.{{citation needed}} This is similar to the premise of [[2585: Rounding]].

This gross error is the result of repeatedly misinterpreting the number of square units as the side length of a square, thus increasing the described area by the power of two. The chain also involves converting between an imperial unit and a metric unit, alternating, thus introducing smaller rounding errors even while switching which measurement is "a single square with sides of a certain distance" and which is "the number of squares that are each of unit length". The upshot is that, while each statement has two roughly similar measurements of area, the chain of misunderstanding ends up claiming ever larger relative expanses. The later participants in this chain also clearly forget to sanity-check their figures, blithely informing others that an individual insect is effectively consuming impossibly huge quantities of food, and travelling enormous linear distances every day to do so.

The title text tells us that [[Randall]] once found an 80-fold error in a reported distance in a published source.

===Table of conversions===
{{note|Table is too wide. "Acre" starts to overlap normal page area, everything else is beyond it. Suggest perhaps three or four significant figures ''plus'' scientific exponentiation on all figures where this does not increase a cell's minimum required width?}}
{| class="wikitable"
! step !! percentage gain !! total percentage gain !! square inch !! square cm !! square foot !! acre !! square meters !! square kilometers !! square miles
|-
! 1
| N/A || N/A ||style="background-color:lightgreen;"| 1||style="background-color:red;"| 6.4516 || 0.00694444444 || 1.5942251e-7 || 0.00064516 || 6.4516e-10 || 2.4909767e-10
|-
! 2
| -7% || -7% || 0.93 ||style="background-color:pink;"| 6 || 0.00645835 || 1.4826e-7 || 0.0006 || 6e-10 || 2.3166e-10
|-
! 3
| +600% || +558% || 5.58001 ||style="background-color:lightgreen;"| 36 (6x6)||0.0387501 || 8.8958e-7 || 0.0036 || 3.6e-9 || 1.39e-9
|-
! 4
| +3,600% || +20,000.9% || 200.8804||style="background-color:lightgreen;"|1,296 (36x36) || style="background-color:red;"|1.395003 || 3.20249e-5 || 0.1296|| 1.296e-7 || 5.00388e-8
|-
! 5
| -28.3% || +14,400% || 144 || style="background-color:green;"|929.03 || style="background-color:pink;"|1 || 2.2957e-5 ||0.092903 || 9.2903e-8 || 3.587e-8
|-
! 6
| +87,188% || +125,550.25% || 125,550.251 || style="background-color:lightgreen;"|810,000 (900x900)|| style="background-color:green;"|871.876744||0.0200155359 || 81||8.1e-5 || 3.1274275e-5
|-
! 7
| +103.22% || +12,960,000% || 129,600 || 836,127||style="background-color:lightgreen;"| 900 (30x30) ||0.0206612|| 83.6127||8.3613e-5 || 3.2283e-5
|-
! 8
| +90,000% || +11,664,000,000% || 116,640,000 || 752,514,624||style="background-color:lightgreen;"| 810,000 (900x900) || style="background-color:green;"|18.5950413|| 75,251.4624||0.0752514624 || 0.0290547521
|-
! 9
| +107.55% || +12,545,275,491% || 1.255e+8 || 8.094e+8|| 871,200||style="background-color:lightgreen;"| 20|| style="background-color:green;"|80,937.1 || 0.0809371 || 0.03125
|-
! 10
| +7,907,375% || +992,001,984,003,868% || 9,920,019,840,040 || 6.4e+13|| 68,889,026,666.94 || 1,581,474.44139 || style="background-color:lightgreen;"|6,400,000,000 (80,000x80,000) || 6,400 ||2,471.053814672
|-
! 11
| +0% || +992,001,984,003,868% || 9,920,019,840,040 || 6.4e+13|| 68,889,026,666.94 || 1,581,474.44139 || 6,400,000,000 || style="background-color:lightgreen;"|6,400 (80x80) ||style="background-color:green;"|2,471.053814672
|-
! 12
| +252,928% || +2,509,056,048,112,096,000% || 2.509056e+16|| 1.6187426e+17 || 1.7424e+14|| 4,000,000,000|| 1.6187426e+13 || 16,187,425.69 || style="background-color:lightgreen;"|6,250,000 (2,500x2,500)
|-
|}
The land area of Australia is 7,688,287 square km or 2,968,464 sq mi, making it the 6th largest country on Earth by area. A 2,500 mile square would actually be 2.1 times greater than the land area of Australia, once again having a rounding error.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Arrows point to each consecutive panel.]

:[Megan is looking at her phone, with Cueball standing next to her.]
:Megan: This newly-described insect can devour up to a square inch of grass per day.
:Cueball: Oh, neat.

:[Cueball is speaking to Ponytail.]
:Cueball: ...it eats a square inch, or 6 cm², of grass per day...

:[Ponytail is speaking to Hairy.]
:Ponytail: ...a 6-centimeter (2½ inch) square of grass, or 36 cm²...

:[Arrows now point to each consecutive conversion.]
:Written out of panel: ...a 36 centimeter square, or over a square foot...
:Written out of panel: ...a square foot, or 900 cm²...
:Written out of panel: ...a 900 cm (30 foot) square...
:Written out of panel: ...a 30 foot square of grass (900 square feet)...
:Written out of panel: ...a 900 foot square, or almost 20 acres...
:Written out of panel: ...20 acres (8 hectares, or 80,000 square meters)...
:Written out of panel: ...an 80,000 meter (80 km) square...
:Written out of panel: ...a square 80 km wide, or roughly 2,500 square miles...
:Written out of panel: ...a 2,500-mile square, or twice the land area of Australia, per day...

:[An arrow points from the last conversion to the last panel.]
:[Hairbun is looking at her phone, with White Hat, Danish and Blondie standing next to her.]
:Hairbun: Did you hear about this insect that defoliates the entire land area of Australia twice a day?
:White Hat: Gosh!
:Danish: Wow.
:Blondie: I hope at least it's contained there...

{{comic discussion}}
[[Category:Animals]]
[[Category:Math]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Ponytail]]
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Hairbun]]
[[Category:Comics featuring White Hat]]
[[Category:Comics featuring Danish]]
[[Category:Comics featuring Blondie]]

3048: Suspension Bridge

2025-02-08T13:26:38Z

172.70.91.129: /* Explanation */

{{comic
| number = 3048
| date = February 7, 2025
| title = Suspension Bridge
| image = suspension_bridge_2x.png
| imagesize = 362x365px
| noexpand = true
| titletext = As a first step, they can put in a secondary deck, to help drivers try it out and find out how fun the jumps are. After a while no one will use the old flat deck and they can remove it.
}}

==Explanation==
{{incomplete|Created by a BOT JUMPING ON A BRIDGE - Needs explanation of title text. Do NOT delete this tag too soon.}}

A suspension bridge works by exploiting the strength in tension of a cable, or series of links, in what is ''usually'' described as a {{w|catenary}} curve (but see later) suspended between towers or other elevated positions and firmly anchored to the ground at either end. Such a cable, or parallel cables, can span a large gap, across which an arch (with compressive forces) or cantilever (with compression below and tension above) bridge structure would be more difficult. The slung droop of the connection, and various other issues (the susceptibility to resonance from moving loads, as well as the sheer impracticality of travelling along this link) means that the surface of the usual road (or footway) itself is suspended from this cable by vertical (and perhaps diagonal) suspending stringers of suitable lengths to maintain a more level track. This usually means that the greatest clearance beneath the traversable part of the bridge is not far below the middle of the main curve of the cable, which is often now a more a parabolic shape, due to the weight of the road and the large number of vertical cables required.

Randall suggests 'improving' the suspension bridge by having ''just'' the catenary curve, needing much less structure, and giving an increased clearance for anything passing beneath (in this case, a tall-masted sailboat) if they pass closer to the supporting towers. This, of course, means that the traffic can ''only'' cross upon the cables themselves, in a way that is not explained at all by this side-section view. Due to the steep nature of the way the cable must pass over the supports, this produces a steep gradient up to and then down from the tower which sends traffic temporarily onto a free ballistic trajectory, assuming it has enough speed. This is described as "fun jumps", {{w|Bug_(engineering)#"It's_not_a_bug,_it's_a_feature"|as if it is how bridges ''should'' work}}. This would likely inflict damage on the car, and might result in unfortunate accidents.{{cn}}

The title text suggests a gradual introduction of this new form of bridge, a practice which is common when introducing new large-scale societal changes. According to Randall, the bridges would at first be a sort of hybrid between the old and new design, where any driver could choose between taking the catenary curve or driving along the tried-and-true flat road. As more and more people sample the "fun jumps" path, he claims, word will spread about how much 'better' this path is, and once it's been widely adopted, the flat road will be discontinued. In reality, a more likely result would be that drivers who take the catenary curve quickly spread word about how ''dangerous'' this path is (and/or spread themselves, and their wrecked vehicles, all around the terrain that the bridge is supposed to cross), and any usage would quickly disappear.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

{{comic discussion}}
[[Category:Engineering]]

3032: Skew-T Log-P

2025-01-03T16:24:57Z

172.70.91.129: /* Table with terms */

{{comic
| number = 3032
| date = January 1, 2025
| title = Skew-T Log-P
| image = skew_t_log_p_2x.png
| imagesize = 569x626px
| noexpand = true
| titletext = The most important quantity for meteorologists is of course the product of latent pressure and temperostrophic enthalpy, though 'how nice the weather is' is a close second.
}}

==Explanation==
{{incomplete|Created by a BOT CLEANING UP AFTER DAVE - This needs an explanation. Table not filled out. Also the title text was not mentioned at all. I added a very simple start to this, but nothing about what the product actually means, please expand... Do NOT delete this tag too soon.}}

{{w|Skew-T log-P diagram}}s are commonly used to plot {{w|atmospheric sounding|atmospheric soundings}} collected by {{w|weather balloon|weather balloons}} or {{w|Constant altitude plan position indicator|other}} [https://rmets.onlinelibrary.wiley.com/doi/abs/10.1002/wea.658 methods]. The name comes from the temperature (T) lines being skewed at a 45-degree angle and the pressure (P) lines being logarithmic in scale. Although it ''looks'' very much like a cross-sectional diagram, it shows non-positional information derived from passing (generally) vertically up through the atmosphere from the initial reference location.

Because the diagrams have a lot of lines on them (isobars, isotherms, adiabats, and mixing ratios, and that's before plotting the actual measurements of temperature and dew point temperature), they can be hard to comprehend. The comic pretends to offer an explanation of one such diagram, but most of the explanations are blatantly incorrect or humorous in nature. The diagram appears to have either measurements from two separate weather measurements or the measured temperature and dewpoint from a single balloon, with solid lines for the primary balloon's two streams of data (often disambiguated by the chosen hue of the line) and dashed ones for the secondary set of data (popped balloon(s) falling back down, a separate second survey balloon rising or estimates derived from weather-radar data). See details in the [[#Table with terms|table]] below. Many weather balloons are designed to rupture after reaching a certain height high in the atmosphere.

[[File:Annotated_Skew_T_diagram.png|thumb|An actual Skew-T Log-P diagram, with several real annotations. The X-axis has temperature (blue diagonal lines in diagram) and the Y-axis has pressure in millibars.]]The true design of a Skew-T Log-P diagram is intended to best represent the nature of the weather in any given column of atmosphere. The pressure (vertical axis, with pressure being inversely related to altitude, more or less) is shown as a logarithmic scale (i.e., Log-P) because it makes altitudes nearly evenly spaced. Plotting pressure proportionately (which must also be from top to bottom, to match its general relationship with altitude) would space features out in ways that would be hard to use and interpret, whereas the logarithmic scale is far more pragmatic. The temperature scale is deliberately tilted, rather than orthogonal, which (together with the logarithmic nature of the inverted pressure scale) allows the typical way that temperatures fall with altitude(≈as pressure falls) to trend roughly vertically, give or take the notable changes that are key to understanding the forecast. Other measurement lines, differently skewed and often also curving across the temperature/pressure skewed-log 'grid', represent various other idealistic relationships (where both T and P vary, keeping another measure constant) that are useful references to meteorologists.

Upon this style of graph are plotted the ''actual'' measurements obtained by releasing a weather balloon or through some other sensor. As well as the variation of actual temperatures and pressures, other retrieved and calculated data is plotted, such as the {{w|dew point}}. The dew point, a function of the air's {{w|absolute humidity|water content}}, temperature, and pressure, is where condensation begins. By observing how the actual measurements and dew point line converge and cross, the development and nature of clouds can be tracked and pinned to specific cloud layers. Further details may also be included, such as wind-direction and wind-speed indications (often to the side of the plot) to give a visual cue about possible {{w|wind shear}} and/or to suggest which direction of adjacent weather-station readings may hold clues as to what changes may later blow in above the current site.

In the title text it is stated that "The most important quantity for meteorologists is of course the product of latent pressure and temperostrophic enthalpy, though 'how nice the weather is' is a close second". So it jokes by comparing a non-existent, complicated-sounding product (temperostrophic enthalpy is not actually a thing) with a simple sentence about how nice the weather is.

==Table with terms==
{| class="wikitable"
!Item in comic
!Correct?
!Explanation
|-
| Pressure latitude || No || {{w|Pressure altitude|Pressure ''altitude''}} is the height above a standard datum plane, a theoretical level where the pressure of the atmosphere is 1013.24 millibars (29.921 inHg). It's essentially an estimate of altitude calculated from atmospheric pressure.
|-
| Enthalpic pressure || No || {{w|Enthalpy}} is the total internal energy of a thermodynamic system plus the product of the system's pressure and volume. Essentially, it represents the energy contained in a system, and is independent of the means or sequence of operations that the system went through to achieve its current state.
|-
| Entropic density || No || {{w|Entropy}} is a quantity that shows many physical processes can only go in one chronological direction. An egg can easily be scrambled (increasing its entropy), but it is very difficult to "un-scramble" an egg[[[285: Wikipedian Protester|''citation needed'']]][[Category:Pages using the "citation needed" template]] (which would decrease its entropy). Ordered systems have low entropy, with differences in temperature, pressure, potential energy, or the like. Disordered systems have high entropy, without temperature, pressure, electrical, or other differentials.
|-
| Latent heat of cooling || No || {{w|Latent heat}} is the energy absorbed or released by a system during a '''constant-temperature''' process, like melting, freezing, boiling, or condensing. Cooling is a process of lowering a temperature, and therefore not a constant-temperature process. The humor comes considering the "heat of cooling."
|-
| Isobars || Yes || Lines denoting equal ("{{wiktionary|iso-}}") air pressure ("{{wiktionary|bar-|-bar}}"), probably most often recognized as the indicators of how ground-level pressures change (or not) across the horizontal area depicted on a weather ''map''. In this type of chart, which depicts data obtained from above a single point, it has the same meaning but is instead a pre-existing reference line across which the actual data is plotted, and does not itself indicate the nature of any wind.
|-
| Omnitrophic wind || No || Something "omnitrophic" would apparently be "all-eating", in some scientific sense. An omnitrophic wind would probably be a concerning phenomenon.
Probably a play on something like {{w|geostrophic wind}} ("geo"+"strophic" being from "Earth curving"), a theoretical state of wind that results from an exact balance between the {{w|Coriolis force}} and the {{w|pressure gradient}} force.
|-
| Isomers || No || Different forms of molecules with the same formula, with the atoms or functional groups arranged differently. An example would be propanol, which has three isomers. One of the most common isomers of propanol has its OH functional group in the middle, so is called isopropyl alcohol or isopropanol.
However, these are actually iso'''therm''' lines, representing equal temperature.
|-
| These lines are slightly different because Dave messed them up || No || Indicating isotherms (or, according to the comic, "isomers"), the suggestion is that slightly wrong lines were drawn by Dave and had to be corrected.
The real reason for the not quite identical lines is that the measured temperature at a given pressure can be converted to or from the ''potential'' temperature that the same air would have if at a standard pressure (holding the same amount of heat energy). For practical reasons, both for composing and interpreting the eventual plot, each of the slightly differently skewed isotherms are given, usually in clearly differentiable styles of line.

The "Dave" of the description may be David Bolton, whose 1980 paper introduced a means of calculating the atmosphere's potential temperature<ref>https://journals.ametsoc.org/view/journals/mwre/108/7/1520-0493_1980_108_1046_tcoept_2_0_co_2.xml</ref>.
|-
| Line of constant thermodynamics || No || {{w|Thermodynamics}} is a branch of physics concerned with work, temperature, heat, the way they relate to entropy, energy, enthalpy, and the physical properties of radiation and matter. As a field of study, Thermodynamics does not have '''constant lines,''' except perhaps as a means of describing a consistent avenue of research.
|-
| Uncomfortably moist adiabat || Wrongly placed, unusually qualified|| This labels a segment of isotherm, which is the exact 'opposite' of an adiabat.
An adiabat is a line along which temperature can change for a given mass, without changing the amount of energy. This is primarily made possible by changing the density (by a change in pressure) of the gas. There are typically two types of adiabat, marked for reference on the plot, "dry adiabat" (curves across the isotherms perpendicularly, to create a largely square but slightly curved grid with them), and "moist/saturated adiabat" (the latter's heat-maintaining profile is influenced greatly by the humidity content, and produces graphing lines vastly different from the equivalent "dry" versions). Randall has declared this (erroneous) type of adiabat to be "uncomfortably" moist, so presumably not totally saturated but also not subjectively 'pleasant'.
|-
| Oops, the balloon flew through a ghost || No || Ghosts do not exist.{{cn}} However, one of the purported effects of ghosts (such as in the film *The Sixth Sense*) is a transient/local lowering of temperature around and/or inside them. The line is interpreted as showing a local low temperature encountered at this pressure(/altitude).
This line, however, is probably the dew point line, indicating that in passing through this layer of the atmosphere, a drier band of air was encountered which would theoretically be cooled a lot more before the water-vapor oversaturates it and liquid water droplets form.
|-
| No birds up here :( || Yes* || This point is near the top of the diagram, with an air pressure of about 110 millibar - about 15 kilometers (50,000 feet) above sea level. This is well above the highest [https://peregrinefund.org/explore-raptors-species/vultures/ruppells-vulture flight height of any known bird species]. However, this information is irrelevant to the purpose of a skew-T log-P diagram.
|-
| Track of rising weather balloon || Yes, partially || Although there are other ways of recording these details, this is typically the record of a rising balloon.
However, it would be a track of the balloon through the varying pressures and temperatures that it records (as the second line of this type records the measurements of dew point at each pressure value). Moreover, circumstances that would make the recorded data plot out a neat {{w|figure-eight knot}} (see "Seems bad", below) are very unlikely.
|-
| Track of popped balloon falling back down || Possible, partially || A standard plot track will include two strong lines, as this has, representing not ''two'' balloons but the recorded temperature track ''and'' the dew point track, both against the (altitude surrogate) progressive pressure changes at each pressure-point.
A further pair of tracks as dotted lines could possibly be from a different launch (earlier, later or simultaneous from an adjacent location) as an analytical reference, but ''may'' indeed be the additional results obtained as the scientific package rapidly descends once the balloon pops.
|-
| Meteogenesis || No || The chart purports to show the path of two weather balloons crossing and labels the space between them with a new word. The root "meteo" means something high up (in this case, balloons) and "genesis" means creation. The implication is that a new balloon was created, though no third flight path is shown so it presumably did not fly separately or was not tracked.
In reality, one of the tracks (almost certainly the left one) is the track of the measured dew point. Where the line of the existing conditions cross this line is where the moisture will precipitate out and form clouds, a process that might well be called "{{wiktionary|meteor#English|meteo}}+{{wiktionary|genesis#English|genesis}}", but {{w|Cloud physics|isn't}}.
|-
| Seems bad || Not a common feature || The path of the balloon loops around in the shape of a {{w|figure-eight knot}}, which would indicate very chaotic conditions at that point, if taken as positional informtion
As the actual Skew-T Log-P graph does not record positional information, this is best interpreted as having encountered a fluctuating temperature as the pressure decreases, continuing as something (possibly {{w|Wind shear#Vertical component|vertical wind shear}}, or some form of compression waves, encounter the instruments) creates a temporary increased in external pressure and then circumstances return it to its more typical altitude-induced pressure-drop. Though this is not ''impossible'' to naturally happen, it might even be best interpreted as the instruments being deliberately 'buzzed' by a passing aircraft or rocket, including some intermittent form of thermal backwash as the interfering craft criss-crosses the balloon's physical track in a briefly complex encounter.
 Whatever happened to the temperature/pressure track, it apparently did not significantly change the associated dew-point/pressure track (if the pressure did indeed temporarily rise, the related dew points repeated themselves each time the pressure values were re-encountered).
|-
| Dew point || Wrongly represented || The temperature at which water condenses out of the air, and therefore dew starts to form, given the amount of water vapor in the air. It is shown here as an ''actual'' single point, when it should be a line (typically the leftmost solid plotted line) representing the temperature at which dew should form at any given pressure.
|-
| Humidor || No || In reality, is a {{w|Humidor|container}} that is used maintain a more controllable humidity within which to store smoking products. In the graph, points at the line that is probably representing the dew point, which is represents the ''actual'' humidity encountered.
|-
| Heavyside layer || No || In the metaphysical cosmology of the musical ''Cats'', the Heavyside Layer is a blissful afterlife which all the cats in the musical long for. It is likely included here as a comical misspelling of the {{w|Kennelly-Heaviside layer|(Kennelly-)Heaviside layer}}, also called the E region of the {{w|ionosphere}} that was co-discovered by {{w|Arthur E. Kennelly}} and {{w|Oliver Heaviside}}. This layer is extremely far up in relative atmospheric terms, straddling the {{w|Kármán line|boundary to 'space'}}, and would be shown as a broad horizontal feature significantly above the existing "No birds up here" label, if it all.
The labeled item, in this diagram, is a heavily marked isotherm, or line of constant temperature. Most likely this is the 0°C line, marking the freezing point of water that is of great importance to meteorologists, pilots, etc. With a few caveats, passing 'through' this line marks a transition between any precipitation tending to be liquid rain and of it being snow/hail-forming (or, on passing down through it, to start melting such things), and if the measurement lines ''start'' above-left of this line then any falling (or condensing) water is almost certainly going to appear as one frozen form or other. Above-ground, it suggests important implications of potential ice-formation (affecting ''weight'' and lift dynamics) upon aircraft beyond any given altitude, should the existing moisture load be high and the dew-point be inconveniently close.
|-
| These lines are tilted because the wind is blowing them || No || The wind is not actually a derivable featured of this diagram, which does not have data of either direction or strength of air movement.
These lines are actually dry adiabats (see above), possibly two sets due to a similar renormalized interpretation, as with the isotherms, at a given reference pressure.
|-
| Don't stand here or you might get hit by a balloon || No || On the misguided basis that this is a cross-sectional diagram, this would be the imagined release-point for the balloon(s) involved. And, if you're particularly (un)lucky with the winds, where they eventually fall straight back down to once the balloon has popped.
However, this is a diagram of some measurements ''for'' a location, not directly indicating a range of places you could choose to stand, and the bottom of the lines indicate the conditions ''at'' the release point (and possibly then the point of landing), regardless of where those lines appear to be rooted. To be accurate, the whole width of the the table (and at a 'height' that represents the actual recorded ground-level pressure for that location and time) is where any 'danger' may be, but the person initially releasing the balloon would not normally be too fazed by being struck by a wind-buffetted balloon (if anything, they'd be more concerned at damaging it prior to release). The attached remains of popped balloon that is no longer buoyant wil generally also act as a form of parachute (together with any actual drogue chute) to make any the light (and often well padded) payload descend slowly enough to not be a falling danger.
 Having traveled tens of kilometres up, before gently coming down, the chances of any given balloon landing in any given awkward spot (let alone the point of release) are low. Where possible, the sensor package and the remains of the balloon may be recovered, but the largest danger may instead be the environmental effects of the fragments of burst balloon, scattered to the very winds they were originally measuring.
|-
| Temperostrophic enthalpy (''Title text'') || No || The largely nonsensical first word perhaps could be interpreted as "time-warping", and allude to the varying passage of time experienced by those who do or do not understand these charts, on having to examine them.
|}

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}

:How to interpret a skew-T log-P diagram
:[The comic shows a skew-T log-P diagram. On it are various labels, including isobars, comments, and other interpretations of the diagram.]
:[Left to the diagram is an upwards-pointing arrow with the label "Pressure Latitude". Right to the diagram is a downwards-pointing arrow with the label "Entropic Density". Below the diagram is a right-pointing arrow with the label "Enthalpic Pressure".]
:[Two solid and dashed lines extend from the top line to the bottom line of the diagram.]
:[The remaining various labels are inside the diagram.]

:[Labels on the left:]
:[An arrow pointing to a densive dashed segment attaching to one solid line:] Latent heat of cooling
:[A label lying on one horizontal guide:] — Isobars —
:[An arrow pointing to the intersection of one solid and dashed line:] Omnitrophic wind
:[A label lying on one left-downward guide:] Isomers
:[A label lying on one right-downward guide:] Line of constant thermodynamics
:[An arrow pointing to a solid dashed segment on one left-downward guide:] Uncomfortably moist adiabat
:[An arrow pointing to the same solid line as ‘latent heat of cooling’:] Humidor
:[An arrow pointing to a steep peak on the same solid line:] Oops, the balloon flew through a ghost
:[To adjacent arrows pointing to two left-downward guide not perfectly coinciding to each other:] These lines are slightly different because Dave messed them up
:[An arrow pointing to the end of solid and dashed lines on the bottom line:] Don’t stand here or you might get hit by a balloon

:[Labels on the right:]
:[An arrow pointing to the top line:] No birds up here :(
:[An arrow pointing to one solid line generally:] Track of rising weather balloon
:[An arrow pointing to one dashed line generally:] Track of popped balloon falling back down
:[An arrow pointing to crossing of two solid lines, The area enclosed by which is painted black] Meteogenesis
:[An arrow pointing to a knot on one solid line:] Seems bad
:[An arrow pointing to a dot] Dew point
:[An arrow pointing to a highlighted left-downward guide:] Heavyside layer
:[Text written sideways below the line:] These lines are tilted because the wind is blowing them

==Trivia==
*Even though this comic was released on New Year's Day 2025, it was not a [[:Category:New Year|New Year comic]].
**Only second time this has happened since New Year comics became a regular thing from 2011.

{{comic discussion}}

[[Category:Charts]]
[[Category:Weather]]

3023: The Maritime Approximation

2024-12-18T09:59:37Z

172.70.91.129: /* Explanation */

{{comic
| number = 3023
| date = December 11, 2024
| title = The Maritime Approximation
| image = the_maritime_approximation_2x.png
| imagesize = 265x126px
| noexpand = true
| titletext = It works because a nautical mile is based on a degree of latitude, and the Earth (e) is a circle.
}}

==Explanation==
Mph ({{w|miles per hour}}) and {{w|Knot (unit)|knot}}s (''nautical miles'' per hour) are both units used to express speed, including that of vehicles. Miles per hour are typically used in the {{w|Miles per hour|US, UK and some smaller countries}} for the speed of cars and other similar vehicles, while knots are used by many sailors and pilots to describe the speed of ships and aircraft. Novice sailors or pilots, or those who spend a lot of time on land, may find it helpful to quickly convert between mph and knots, in order to relate to typical ground-surface speeds.

This could be done in the form of 1 knot = 1.2 mph, or 1 mph = 0.87 knots (1 knot = 1.85 km/h and 1 km/h = 0.54 knots for metric navigators). [[Randall]] has humorously noticed that ''π'' mph ≈ {{w|E_(mathematical_constant)|''e''}} knots: ''π'' mph = [https://www.google.com/search?client=firefox-b-d&q=pi+mph+in+knots 2.72997] knots, while ''e'' ≈ 2.71828.

Knots are related to the circumference of the Earth, which can introduce ''π'', but this is only "useful" if you want to express your speed as a fraction of the radius of the Earth: 1 knot = 1 nautical mile per hour = 1/60 of a degree of Earth's circumference per hour = 1/21,600 of Earth's circumference per hour = 2''π''/21,600 x Earth's radius per hour. However, nowadays this is an approximation, because a nautical mile is defined as exactly 1852 m, which is not exactly 1/60 of a degree of Earth's circumference.

The observation of the interesting near identity between MPH and knots in the comic is misleading, because it is not exact, but only correct to a certain percentage, unlike the identity it is compared to: {{w|Euler's Identity}}, which is exact and expresses a deep mathematical insight, which is what makes the latter truly remarkable. The former is nothing but an unimpressive, if mildly interesting coincidence. This isn't helped by the fact that the comic carries the implication that this neat, easy-to-remember identity is actually useful for sailors, when really, being easy to remember is all it has going for it: it doesn't make calculations any easier, it is impossible to do without a calculator or paper, and doing it on paper is much harder than other conversions, given that ''π'' and ''e'' are both {{w|Irrational number|irrational}} and {{w|Transcendental number|transcendental}}. Finally and most importantly, this conversion between knots and MPH is far far less accurate than the typical conversion factor used, i.e. 1.1508, which is accurate to within 0.00179%; about 280x better than Randall's. This can make a huge difference on shipping routes, which can be hundreds or thousands of miles long.

The title text furthers the joke that this identity between MPH and knots is truly fundamental, but through faulty logic. Whenever ''π'' shows up in an equation, the claim made by many mathematicians is that there is a circle hiding somewhere in the math. Randall says that ''π'' is coming from the fact that nautical miles are based on the fact that the Earth is round, and shipping routes over its surface are circular. As profound as this sounds, it makes no mathematical sense at all. He also claims that ''e'' is in the equation because 'Earth' starts with an E, which is nothing but word play.

The equality shown in this strip consists of several different parts:

# The mile (1609.344 m) per hour (mph) is a unit of speed common for motor vehicles in a few countries, such as the United States and United Kingdom.
# The knot is a unit of speed that is one nautical mile (1852 m) per hour, used in nautical contexts.
# ''π'' is a number equal to the ratio of a circle's circumference to its diameter, about 3.14159.
# ''e'' is Euler's number, the base of the natural logarithm, about 2.71828.

''π'' mph × (1609.344 meters/statute mile ÷ 1852 meters/nautical mile) ≈ 2.729969 knots. The result is only about 0.43% larger than ''e'' knots ≈ 2.71828 knots.

Randall has in the past made similar observations of different dimensions that equal each other with comics such as [[687: Dimensional Analysis]], where he compares {{w|Planck energy}}, the pressure at Earth's core, the gas mileage in a Prius, and the width of the English Channel to ''π''. In addition, in [[What If?]], he has compared the mass of Earth to be ''π'' "milliJupiters," or ''π'' times the mass of Jupiter divided by 1000, and noted that the volume of a cube with side lengths of one mile is roughly similar to the volume of a sphere with a radius of 1 kilometer. In [[217: e to the pi Minus pi]] and [[1047: Approximations]], Randall gives a lot of similar numerical approximations.

Arguably, as safe operating speeds for particular aircraft/watercraft may bear little relationship to (for example) road vehicle speeds, it might be better just to develop a separate 'air sense' (perhaps mostly at higher velocities, far above any landmark that you might pass by) or 'water sense' (often at lower velocities, and with the particular fluid nature of the water's surface) that is keyed especially to the knots-rated speed of your vessel, without attempting to carry over this aspect of any pre-existing 'road sense'. One hopefully ''rare'' exception might possibly be in the event of a plane having to make an emergency landing on a public highway, where it could be useful to know if a (possibly unpowered) plane's final landing speed can be made to be not too far off that of any unsuspecting road traffic that you may have to land in the midst of; but this would never be a trivial endeavour in any case, and even having to attempt such a feat probably means you have few options open to you and very little time to consider many of these finer details.

==Transcript==
:[In a small panel an equation is shown. There is a footnote below the equation:]
:<big>π mph = ''e'' knots*</big>
:*Correct to <0.5%

:[Caption below the panel:]
:The sailor's version of eiπ=−1

{{comic discussion}}

[[Category:Math]]