explain xkcd - User contributions [en]

2675: Pilot Priority List

2022-09-21T22:48:00Z

FranchuFranchu: Make proper ordered list

{{comic
| number = 2675
| date = September 21, 2022
| title = Pilot Priority List
| image = pilot_priority_list_2x.png
| imagesize = 369x548px
| noexpand = true
| titletext = CELEBRATE: Serve passengers tiered cakes shaped like the airspace class diagram
}}

==Explanation==
{{incomplete|Created by a SUBLIMATING PILOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

The "ANC" Pilot Priority Checklist is a list of three guidelines, sorted by priority, that pilots should follow to prevent them from being distracted. Failing to follow it might make the plane crash or suffer other problems.

Randall humorously "expands" this list with things that pilots should do if they have nothing to aviate, navigate, or communicate. These extra tasks go from somewhat hilarious to physically impossible or dangerous. In real life these actions should not be taken as they would distract the pilot and prevent him/her from reaching the cabin in case of an emergency.

# Aviate means "Keeping the plane in control". If the pilot fails to do this the plane might crash. That is why this should be the highest priority for the pilot.
# Navigate means "Knowing where you are and where you're going". Failing to follow this might make the plane go into restricted airspace, for example, or make the journey take too long.
# Communicate means talking to air traffic control (ATC) through radio. In the standard list this is the lowest priority because talking through the radio might distract the pilot from other more important or urgent tasks.

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

{{comic discussion}}

2675: Pilot Priority List

2022-09-21T22:46:44Z

FranchuFranchu: Added a simple explanation

{{comic
| number = 2675
| date = September 21, 2022
| title = Pilot Priority List
| image = pilot_priority_list_2x.png
| imagesize = 369x548px
| noexpand = true
| titletext = CELEBRATE: Serve passengers tiered cakes shaped like the airspace class diagram
}}

==Explanation==
{{incomplete|Created by a SUBLIMATING PILOT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

The "ANC" Pilot Priority Checklist is a list of three guidelines, sorted by priority, that pilots should follow to prevent them from being distracted. Failing to follow it might make the plane crash or suffer other problems.

Randall humorously "expands" this list with things that pilots should do if they have nothing to aviate, navigate, or communicate. These extra tasks go from somewhat hilarious to physically impossible or dangerous. In real life these actions should not be taken as they would distract the pilot and prevent him/her from reaching the cabin in case of an emergency.

1. Aviate means "Keeping the plane in control". If the pilot fails to do this the plane might crash. That is why this should be the highest priority for the pilot.
2. Navigate means "Knowing where you are and where you're going". Failing to follow this might make the plane go into restricted airspace, for example, or make the journey take too long.
3. Communicate means talking to air traffic control (ATC) through radio. In the standard list this is the lowest priority because talking through the radio might distract the pilot from other more important or urgent tasks.

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

{{comic discussion}}

2639: Periodic Table Changes

2022-06-29T22:39:26Z

FranchuFranchu: Write a simple explanation of the general joke in the comic.

{{comic
| number = 2639
| date = June 29, 2022
| title = Periodic Table Changes
| image = periodic_table_changes.png
| titletext = It's nice how the end of the periodic table is flush with the edge these days, so I think we should agree no one should find any new elements after #118 unless they discover a whole row at once.
}}

==Explanation==
{{incomplete|Created by a SPITE ELEMENT - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

The [https://en.wikipedia.org/wiki/Periodic_table periodic table] is a table used to arrange [https://en.wikipedia.org/wiki/Chemical_element chemical elements] according to their chemical and physical properties. This comic proposes "changes" to the periodic table that would be more pleasant aesthetically or make the periodic table look more regular. However, some changes don't take into account that elements would stop being arranged by their properties and the periodic table would stop being useful after such changes.

Other modifications make up new elements or remove existing ones from the table, which would not be a reasonable decision given that the periodic table is supposed to include all existing elements, whether they make the table neater or they don't.

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

{{comic discussion}}

2228: Machine Learning Captcha

2019-11-14T00:56:28Z

FranchuFranchu: Basic explanation

{{comic
| number = 2228
| date = November 14, 2019
| title = Machine Learning Captcha
| image = machine_learning_captcha.png
| titletext = More likely: Click on all the pictures of people who appear disloyal to [name of company or government]
}}

==Explanation==
{{incomplete|Created by a HUMAN CAPTCHA. Please mention here why this explanation isn't complete. Do NOT delete this tag too soon.}}
CAPTCHAs are a challenge used to prove the user is a human and not an automated program. Machine learning is a process used to train AIs to do specific tasks. This comic jokes about a trained AI which wants to dominate the world. In order to prevent people from taking shelter, the AI asks humans to tell places they would hide in a CAPTCHA. Then this AI will get ready in case someone hid there

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

:[Cueball, seated before a desk, is staring at a computer; one hand is on his lap while the other is poised over his keyboard. A line is drawn from the computer screen, showing what is displayed on it.]
:Computer: To prove you're a human, click on all the photos that show places you would run for shelter during a robot uprising.

:[The computer then gives nine images arranged in a 3 by 3 square; from left to right and top to bottom, they are a house, some trees, a window{{Dubious}}, a car, a skyline, a crosswalk{{Dubious}}, a log and board{{Dubious}}, a mailbox, and a hole.]

{{comic discussion}}
[[Category:Comics featuring Cueball]]
[[Category:Artificial Intelligence]]
[[Category:Programming]]
[[Category:Robots]]

1247: The Mother of All Suspicious Files

2019-08-05T20:09:57Z

FranchuFranchu: Fixed broken Wikipedia link

{{comic
| number = 1247
| date = August 5, 2013
| title = The Mother of All Suspicious Files
| image = the_mother_of_all_suspicious_files.png
| titletext = Better change the URL to 'https' before downloading.
}}

==Explanation==
The save {{w|dialog box}} shows a download from <tt><nowiki>http://65.222.202.53</nowiki></tt>, an {{w|IP address}} that hosted {{w|JavaScript}} {{w|malware}} during a recent attack on the {{w|Tor anonymity network}}, with a very long file title. Many of the {{w|file extension|extensions}} used inside there indicate executable code; multiple file extensions are sometimes used to disguise a {{w|Trojan horse (computing)|trojan program}} as a document.

You can also see common download syntax for a pirated movie, {{w|Hackers (film)|''Hackers''}}, likely included to appear malicious to anyone skimming but is actually a movie about hackers, making it a benign reference rather than malicious. It is described as "<tt>_BLURAY_CAM</tt>", which contradicts itself ("<tt>_BLURAY</tt>" would imply it was ripped from a copy on {{w|Blu-ray Disc}}, while "<tt>_CAM</tt>" would mean it was copied by pointing a camera at the screen in the cinema). "<tt>_BLURAY_CAM</tt>" would probably indicate a search-keyword-stuffed fake copy; fake pirated media often contain viruses (although this is more likely to be a problem with newer media, before the first real pirated copy appears).

The {{w|URL}} contains the path "<tt>~tilde/pub/cia-bin/etc</tt>". The first part is a public folder of a user named "tilde" (which is also the name for the {{w|tilde|~ symbol}}), "<tt>cgi-bin</tt>" is a common folder on a web server for server-side executables ([[Randall]] changes the name to "<tt>[[CIA|cia]]-bin</tt>"), and "<tt>etc</tt>" is a standard folder for configuration files – normally never accessible through a web server. The program "init.dll" isn't executable at all, it's a {{w|Windows Dynamic Link Library}} which can't be run standalone, and is rarely referenced in URLs (even though such syntax is still being employed, even on [https://www.google.com/search?q=site:edu+filetype:dll reputable websites (Google search)] or here at [https://signin.ebay.com/ws/eBayISAPI.dll eBay], indicating the webserver is a Microsoft {{w|Active Server Pages|ASP}} server). The question mark indicates the start of a parameter list, and in this case we have only one named "<tt>FILE</tt>".

The "Save" button is greyed out, suggesting that it is disabled; you can click only the "Cancel" button. For security reasons, some browsers (like Firefox) disable the "Save" button for a few seconds before enabling it. This prevents users from accidentally accepting a download while entering input, like a malicious CAPTCHA.

The complete content sent to the server, starting with "<tt>/~tilde...</tt>" and ending with "<tt>...out.exe</tt>", is exactly 256 characters long. On {{w|HTML 3}} specifications you have a limitation of 1024 characters, whereas later HTML specifications don't have this limit; it just depends on the web server's capabilities. But posting parameters directly at the URL is still a worse choice.

The content of the parameter is shown here:
*<tt>__</tt> (underscore underscore) — used in the {{w|C programming language}} to denote that a symbol is really not for public consumption.
*<tt>{{w|autoexec.bat}}</tt> — a {{w|batch file}} which is automatically run during startup on {{w|MS-DOS}} and {{w|Windows}} operating systems, and was often modified by viruses, which added malicious code to be run on each boot.
*<tt>My%20OSX%20Documents</tt> — referencing Apple's {{w|OS X}} operating system (<tt>{{w|URL encoding#Character data|%20}}</tt> is a representation of a space in a URL, i.e. it reads as "<tt>My OSX Documents</tt>").
*<tt>install.exe</tt> — a typical {{w|Installer#Installer|installer}}.
*<tt>{{w|RAR|.rar}}</tt> — a compressed archive file type.
*<tt>{{w|INI file|.ini}}</tt> — a configuration file type.
*<tt>{{w|Tar (computing)|.tar}}</tt> — a {{w|file}} archive popular in {{w|Unix}} and {{w|Unix-like}} operating systems. tar has been mentioned [[1168: tar|before]].
*<tt>.doçx</tt> — <tt>{{w|docx|.docx}}</tt> is an {{w|Office Open XML}} file, i.e. a word processing format used by {{w|Microsoft Word 2007}} and above, but has no {{w|cedilla}} (¸). The addition of a cedilla may be a reference to exploits that rely on rare characters being mistaken for more common ones that look similar, such as the {{w|IDN homograph attack}}.
*<tt>.phphphp</tt> — a play on {{w|PHP}} files, a kind of server-based web page file type. PHP originally stood for "Personal Home Page" but was later redefined as the recursive abbreviation "PHP: Hypertext Preprocessor".
*<tt>{{w|XHTML|.xhtml}}</tt> — another web page file type.
*<tt>{{w|TransducerML|.tml}}</tt> — stands for Transducer Markup Language, an {{w|XML}}-based {{w|markup language}} that specifies how to capture, time-tag and describe sensor data.
*<tt>.xtl</tt> — possibly a play on XHTML.
*<tt>.txxt</tt> — a play on <tt>{{w|Text file|.txt}}</tt> file types.
*<tt>0DAY.HACK</tt> — a reference to a {{w|zero-day exploit}}. (overlaps with the next entry)
*<tt>HACK.ERS_(1995)_BLURAY_CAM-XVID</tt> — a reference to the 1995 {{W|Hackers (film)|''Hackers''}} movie, but pirated movies would either be a <tt>BLURAYRIP/DVDRIP</tt> or <tt>CAM</tt>, but not both at the same time unless you used a camera to record a {{w|Blu-Ray}} movie as it played.
*<tt>{{w|EXE|.exe}}</tt> — an executable file type used by Microsoft Windows.
*<tt>[SCR]</tt> — a tag used by movie pirates to denote a '{{w|Screener}}', the DVD copy of films given to critics prior to theater release. Usually the highest quality available at the time, rare, and thus good bait for a virus-laden download. "{{w|.scr}}" is also the extension for screensaver files, really just an exe file with a different extension and one of the classical ways to distribute infected files.
*<tt>{{w|Lisp (programming language)|Lisp}}</tt> — programming language.
*<tt>{{w|Windows Installer|.msi}}</tt> — an installation file used by Microsoft Installer.
*<tt>{{w|.lnk}}</tt> — an extension used by Microsoft Windows for shortcuts. The extension is normally hidden to the user.
*<tt>.lnk.zda.gnn</tt> — references to {{w|Link (The Legend of Zelda)|Link}}, {{w|Princess Zelda|Zelda}}, and {{w|Ganon}}, important characters from ''{{w|The Legend of Zelda}}'' video game franchise.
*<tt>{{w|White Rabbit#Television and films|wrbt.obj}}</tt> — A reference to the line of code Dennis Nedry used in ''{{w|Jurassic Park}}'' to shut down key systems.
*<tt>{{w|Object file|.o}}</tt> — The extension for a {{w|Linker (computing)|linker file}}, an intermediary created when compiling {{w|C programming language|C code}}.
*<tt>{{w|Header file|.h}}</tt> — The file extension of a {{w|header file}} in C code.
*<tt>{{w|.swf}}</tt> — {{w|Shockwave Flash}} file type.
*<tt>{{w|Dpkg|.dpkg}}</tt> — The {{w|Debian}} package management, although the package files use the file suffix <tt>.deb</tt>.
*<tt>.app</tt> — an application on the {{w|Mac OS X}} operating system.
*<tt>{{w|ZIP (file format)|.zip}}</tt> — compressed archive file type.
*<tt>.co</tt> — the {{w|List of Internet top-level domains|top-level domain (TLD)}} for Colombia, but marketed as a global domain. Some countries use <tt>.co.''TLD''</tt> for general use, e.g. <tt>.co.uk</tt> in the United Kingdom. But the TLD <tt>.gz</tt> does not exist and thus <tt>.co.gz</tt> is invalid.
*<tt>{{w|Gzip|.gz}}</tt> — a compressed file using {{w|GNU}} zip.
*<tt>{{w|A.out|.a.out}}</tt> — Default filename when creating an executable on {{w|Linux}} or other Unix-like operating systems if none was specified for the compiler.

The title text suggests changing from <tt>http</tt> to <tt>https</tt>, as if encrypting a suspicious file before downloading it is somehow better than downloading it unencrypted. <tt>{{w|http}}</tt> (Hypertext Transfer Protocol) and <tt>{{w|https}}</tt> (Hypertext Transfer Protocol – Secure) are the two common protocols for getting web pages and web downloads. http is the simple download, whereas https adds an SSL encryption layer so the item being downloaded cannot be viewed unencrypted by anyone except the end recipient. Changing <tt>http</tt> to <tt>https</tt> is a common suggestion to improve security when browsing the web from an insecure network (such as a public {{w|WiFi}} hotspot) to avoid surveillance or hijacking to a malicious website; Google automatically switches to <tt>https</tt> for all mail accounts and is starting to do so with searches. The end recipient will still get whatever nasties were in the original, however — encrypting it doesn't change the content at all.

The {{w|IP address}} referenced in the comic, <tt>65.222.202.53</tt>, is currently being used by the shellcode of a {{w|JavaScript}} {{w|zero-day exploit}} for the {{w|Tor Browser Bundle}} being run by the {{w|FBI}} to phone home over the clearnet [http://thehackernews.com/2013/08/Firefox-Exploit-Tor-Network-child-pornography-Freedom-Hosting.html] and deanonymize visitors to websites on Freedom Hosting that are serving child pornography. [http://www.reddit.com/r/onions/comments/1jmrta/founder_of_the_freedom_hosting_arrested_held/]

As the last extension in the file is .exe, a Windows computer would run the file like an application, usually, it is not safe to run unknown .exe files

==Transcript==
:[Browser download warning box containing the following text.]
:WARNING!
:This type of file can harm your computer! Are you sure you want to download:
:<nowiki>http://65.222.202.53/~TILDE/PUB/CIA-BIN/ETC/INIT.DLL?FILE=__AUTOEXEC.BAT.MY%20OSX%20DOCUMENTS-INSTALL.EXE.RAR.INI.TAR.DOÇX.PHPHPHP.XHTML.TML.XTL.TXXT.0DAY.HACK.ERS_(1995)_BLURAY_CAM-XVID.EXE.TAR.[SCR].LISP.MSI.LNK.ZDA.GNN.WRBT.OBJ.O.H.SWF.DPKG.APP.ZIP.TAR.TAR.CO.GZ.A.OUT.EXE</nowiki>
:[Cancel and Save buttons (Save button disabled)]

{{comic discussion}}
[[Category:Comics with color]]
[[Category:Computers]]
[[Category:Video games]]

2049: Unfulfilling Toys

2018-09-21T15:31:01Z

FranchuFranchu: /* Rigid Slap Bracelet */

{{comic
| number = 2049
| date = September 21, 2018
| title = Unfulfilling Toys
| image = unfulfilling_toys.png
| titletext = We were going to do a falling-apart Rubik's cube that was just 27 independent blocks stuck together with magnets, but then we realized it was actually really cool and even kind of worked, so we cut that one.
}}

==Explanation==
{{incomplete|Created by a Stretch Armstrong made out of hard plastic. Please edit the explanation below and only mention here why it isn't complete. Do NOT delete this tag too soon.}}

This comic lists and illustrates a number of classic toys that are missing a key piece of that makes them work or that makes them unique. As such, they are not much fun.

====Rigid Slap Bracelet====
Slap Bracelets are flexible bars that when you hit it in your arm they twist and become a bracelet. A rigid one would not twist and would be deeply frustating

====Sealed Stomp Rocket====

====Pump-only Supersoaker====
A supersoaker is a water gun that works by first pumping air into the gun, which introduces air pressure next to the water, then releasing the water using the gun's trigger -- the extra pressure from the pumped air makes the water go much further than a regular water gun. In this version, the water cannot be released, so the fun part of the water gun -- getting to spray your friends -- isn't there.

====Glass Glow Stick====

In a classic glow-stick, made of flexible plastic, one much first bend it enough that something inside (which might be glass or some other hard crack-able substance) cracks, which allows chemicals to mix and begin glowing within the plastic tube. If the entire tube were made of actual glass, however, if would simply crack in half or pieces and would just make a mess.

====Wingless Sky Dancer====

====No-strings-attached Yo-yo====
This one actually exists and some people are even quite good at it. See https://www.youtube.com/watch?v=t5P-fdrlBg8 for example.

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

{{comic discussion}}

994: Advent Calendar

2017-11-08T01:34:29Z

FranchuFranchu: /* Explanation */

{{comic
| number = 994
| date = December 23, 2011
| title = Advent Calendar
| image = advent_calendar.png
| titletext = I think you could get up to about 11:59:57 before you'd have trouble swallowing the chocolates fast enough. At that point, you'd need some kind of a liquify-and-chug apparatus to get up over the 11:59:59 barrier. Anyway, Merry Christmas!
}}

==Explanation==
An {{w|Advent calendar}} is a special calendar used to count or celebrate the days in anticipation of Christmas. They come in a multitude of forms, from a simple paper calendar with flaps covering each of the days, to fabric pockets on a background scene, to painted wooden boxes with cubby holes for small items. Advent calendars typically take the form of a large rectangular card with "windows", of which there are usually 24: one for each day of December leading up to and including Christmas Eve (December 24). Consecutive doors are opened every day leading up to Christmas, beginning on December 1. The calendar windows open to reveal an image, a poem, a portion of a story (such as the story of the Nativity of Jesus), or a small gift, such as a toy or a chocolate item.

This comic, however, depicts an Advent calendar which has a chocolate every time they get halfway to Christmas. This is a joke because of {{w|Zeno's paradox}}, which said "Before a moving object can travel a certain distance, it must travel half that distance. Before it can travel half the distance it must travel 1/4 the distance, etc. This sequence goes on forever. Therefore, it seems that the original distance cannot be traveled, and motion is impossible." This means that eating chocolates at diminishing intervals will make it so Christmas never happens.

The title text says that when you get close to midnight, it gets physically impossible to eat the chocolates that fast, but you could get the one second away mark with a chocolate liquefier and feeder tube.

Going from the second to the last of the visible time stamps it goes like this: At 11:57:11.25 PM there is still remaining 00:02:48.75 (2 minutes 48 seconds and 75 hundredth of a second.) Half of this time period will then progress before the next windows time stamp, that is 00:01:24.375 (1 minute and 24.375 s). This will then give the next time stamp by adding to the previous and we get: 11:58:35.625 PM. This has been rounded to 35.63 s in the comic. Similarly the time stamp for the next four windows, whose top are visible below, can be calculated starting from the fact that there is now only 00:01:24.375 left of the day.

*13: 42.1875 s left, so the time stamp is: 11:59:17.8125
*14: 21.09375 s left, so the time stamp is: 11:59:39.90625
*15: 10.546875 s left, so the time stamp is: 11:59:49.453125
*16: 5.2734375 s left, so the time stamp is: 11:59:54,7265625

It would take three more windows before crossing the 11:59:59 line with less than one second to go. At the 19th window there would only be 0.6591796875 seconds left of the day for a time-stamp of 11:59:59.3408203125. So that would be a window another line further down, even below the green window (no. 15) that is just visible at the button of the panel. And you would have to eat four chocolates in less than five seconds from window no. 16 to fulfill Randall's prediction.

When reaching the 24th window there would be 0.0206 s left, so that is 6 chocolates in 0.638 s. That may be a good place to stop, but of course you could continue at least until reaching the {{w|Planck time}} of 5.39 x 10-44 s. That limit will not be reached before window 162, so there are still 138 chocolates left for those last two hundredths of a second. Planck's time will be reached on window 1.8347299 x 1024.

[[1153: Proof]] is also about Zeno, and [[1577: Advent]] is a very different longer running Advent calendar (but with only a finite number of windows).

==Transcript==
:[A portion of an advent calendar shows 12 windows where the date can be seen below. The top row is cut off so you cannot see the very top of the window At the bottom there are four more windows, but only the top part can be seen, and there is no decoration visible. All the other windows have a decoration, although, you cannot see the one on the second window as it is opened more than 90 degree. The first is also opened, but not more than you can see there is a decoration. The 3rd is also open. The rest is still closed.]
:[A green mistletoe on red, partially open.]
:December 23rd

:[A fully open window.]
:December 24th 12:00 AM

:[A red and white Santa hat on green just opened.]
:December 24th Noon

:[Two crossed red and white candy canes on white. From here all windows are closed.]
:December 24th 6:00 PM

:[A red Christmas ball on white.]
:December 24th 9:00 PM

:[A white Christmas star on red.]
:December 24th 10:30 PM

:[A red Christmas heart on gren.]
:December 24th 11:15 PM

:[A red Santa sleigh on white.]
:December 24th 11:37:30 PM

:[A red and white Christmas sock on green.]
:December 24th 11:48:45 PM

:[A green Christmas tree on red.]
:December 24th 11:54:22.5 PM

:[A red and green Christmas wreath on white]
:December 24th 11:57:11.25 PM

:[A red and white Christmas gift on green]
:December 24th 11:58:35.63 PM

:[Below the top of four more windows where only the background colors can be seen red, white, green and then red again.]

:[Caption below the panel:]
:'''Zeno's Advent Calendar'''

{{Comic discussion}}
[[Category:Comics with color]]
[[Category:Christmas]]
[[Category:Philosophy]]
[[Category:Time]]