Talk:3038: Uncanceled Units

DUDE I'M STILL IN SCHOOL RN, WHAT? (also, the joke is that energy is power*time, so kWh is kJ/s... in an hour Caliban (talk) 13:27, 15 January 2025 (UTC)

I guess not every comic can be a winner. Talking about an appliance using a certain amount of kWH per day is clear and normal. Power gets billed by the kWh, not the Joule. While technically not wrong, wanting "cancel" a sub-part of the commonly-used energy unit kWh and leaving it in deliberately-obscured units most people are less familiar with is the sort of insanity I'd more expect from White Hat than Cueball. 172.70.35.171 13:39, 15 January 2025 (UTC)

Maybe that is a meta-joke? To frame kWh/day as something crazy by giving that line to whitehat --Lupo (talk) 13:52, 15 January 2025 (UTC)

There's a difference between instantaneous power draw, and the total "volume"(/area, really) of power over time. Though a fridge is "always on", it is still only irregularly at full-draw. But, to the power company (or to the gas company, who will generally give a kWh measure of 'energy taken from the network'), they don't (generally) care whether you used twice as many kW over half the time or half as many over twice the time, within any given total billing period, even if it affects what you think. 172.70.163.46 14:39, 15 January 2025 (UTC)

Using joule as if it was an everyday unit of energy would be weird but I don't agree that watt is crazy. It's a normal unit of energy consumption that does mean something to people, e.g. 1000W microwave, 100W (incandescent) light bulb. Don't get me wrong kWh/day is also useful to translate it to your energy bill, but I do feel slightly uncomfortable every time I see that time divided by time :-) Mtcv (talk) 14:40, 15 January 2025 (UTC)

I don't think the complaint is that it's unclear, it's that Cueball/Randall instinctively wants units simplified - as they would be in a science context rather than a useful-for-normal-people's-everyday-needs context. 108.162.238.183 02:40, 16 January 2025 (UTC)

This is especially funny with US units. My car needs about 5l/100km, or 0.05mm². Now I am wondering how many ft^(-2) my car does... --Lupo (talk) 13:49, 15 January 2025 (UTC)

You make a good point about the units (at least in one instance). Shouldn't the reduced units for fuel economy be inverse area? Effectively, it is a measure of the distance the vehicle could travel while consuming a column of fuel with a specific height and specific top (or bottom) surface area. Or, The better the fuel economy, the less the surface area that is necessary to move a specific distance. SammyChips (talk) 20:41, 15 January 2025 (UTC)

It depends on what the original unit is. In my country (Germany) we measure it in volume/distance, which would reduce to area. North American convention is in distance/volume which would reduce to inverse area. Good thing about distance/volume is that "high number = good". However I think outside of escaping from a nuclear disaster or in a zombie apocalypse it isn't a really helpful thing to know. Because how often do you know "I got x amount of fuel. Wonder how far I can get." But you will likely be in the situation where you quickly want to see "How much fuel do I need to get to place x which is y distance from here". --Lupo (talk) 21:57, 15 January 2025 (UTC)

how often do you know "I got x amount of fuel. Wonder how far I can get." Quite often, because the question I'm really asking is whether I can get where I'm going with some margin built in before I need to refuel my car. When I do refuel or recharge the car, I'll go to 100% of capacity. I just want to know whether I have to do that now or if I can wait and do it later because later would be more convenient. The only time I want the number the other way is when I'm buying a car and want to make it as efficient as possible. Once I have it, the amount of fuel I need isn't going to change.Yttrium (talk) 09:02, 16 January 2025 (UTC)

Mhh... probably a question of what one is used to. If I need to go 400 km, and I know my car uses 5l/100km, I just multiply 4*5 to see that I need 20l, and will know if what I have is enough or not. But I guess with mpg you can do a just as easy calc: If my car gets 50mpg (roughly 5l/100km) and I have 5 gallons (roughly 20l), I can go 50*5=250 miles, which is roughly 400km. My nitpick is: My car, and I think all cars I ever drove just shows me a dial from empty to full. Knowing how much "full" is, I can estimate how much gas I have, while my GPS will tell me a pretty exact number of km I need to go. So if I am fuelling up on a monday morning (where gas tends to be more expensive in my area than on other times), or fuel up right before I get my next salary, I might just put in as much as I need right now. But yes, maybe/probably it is mostly a thing about habits and what you are used to. And might be more of an European issue, since fuel is basically free in North America in comparison. So I guess everyone just fuels up fully all the time, but has to be cautious to reach the next gas station when travelling through the more sparely-populated areas...--Lupo (talk) 10:19, 16 January 2025 (UTC)

More usefully imagined as the front (or back) end of a horizontal column (or, twisting as it may, a pipeline) that traverses the journey made by the vehicle. As if (instantaneous variations excepted) you consume precisely the fuel that your vehicle passes 'through/around'. 141.101.76.92 20:45, 15 January 2025 (UTC)

Yeah. Maybe we should express fuel consumption in terms of the speed fuel needs to be drawn through a standard fuel line. SammyChips (talk) 21:01, 15 January 2025 (UTC)

fridge 172.70.126.147 14:22, 15 January 2025 (UTC)

The late Sir David MacKay wrote an excellent book, Sustainable Energy – without the hot air (which is available free online). On this page he talks about the units he uses in the book: kWh for energy ("one unit") and kWh/day for power - becuase it's simple for lay-people to understand - how many units does this appliance use per day. It's a good book if any of you are interested in sustainable energy (although it was written in 2008, so some bits might be out of date by now) 172.70.85.33 (talk) 14:33, 15 January 2025 (please sign your comments with ~~~~)

If anyone's curious, I found an online gallons per square foot calculator: https://www.omnicalculator.com/construction/gallons-per-square-foot 172.71.223.6 15:54, 15 January 2025 (UTC)

The answer to Cueball's question is likely NO in the US and YES in the UK, due not just to gallon size but also fridge size (a model like that is a particularly large fridge, when I bought one 10 years ago going for the smallest available I had to modify my cabinet above the fridge as there wasn't one less than 6'8"- the fridge hole was 6' previous).Seebert (talk) 16:02, 15 January 2025 (UTC)

I disagree with this comic, and I think the final paragraph in the explanation about Hubble's constant best explains why. Beanie ^talk 15:57, 15 January 2025 (UTC)

It doesn't make any sense to 'disagree' with an observation.141.101.98.245 09:36, 16 January 2025 (UTC)

Technically, kWh should be written as kW⋅h or kW h, because it literally means "kilowatts multiplied by one hour", not "kilowatts per hour" as many people assume. However, almost nobody writes it correctly. (kW/h is sometimes also seen, but egregiously incorrect.) Also, particularly now that electric vehicles are becoming more popular, people often get confused between kW and kW h. The car can charge at a peak or average rate expressed in kW, but energy billed by a charging service provider is expressed in kWh. People frequently either add or remove the "h" incorrectly because they don't understand the difference. In some places like India, a kilowatt-hour is simply referred to as a "unit" to avoid confusion. In my opinion, it was an enormous mistake to use kWh when we could be using mJ instead, which I think is probably something close to the point Randall may have been trying to make. Anyway, I wasn't sure if there was a place for any of this random trivia in the article itself, but feel free to use it. Equites (talk) 17:11, 15 January 2025 (UTC)

Relevant XKCD… I mean relevant YouTube video: "Cursed units" 1 and 2: https://www.youtube.com/watch?v=kkfIXUjkYqE https://www.youtube.com/watch?v=Zg7xe8MkJHs Fabian42 (talk) 17:31, 15 January 2025 (UTC)

Highly relevant, in fact. The first video referred to the kilowatt-hour as "cursed", which became a highly polarizing issue in the comments, something that was addressed at the beginning of part 2. Assuming these responses weren't cherry-picked, I get the impression that there are a lot of people on both sides of this. It seems like the same kind of thing we're seeing in this very comment section. ISaveXKCDpapers (talk) 18:10, 15 January 2025 (UTC)

I always wonder why people here prefer liter/m^2 for the amount of rain. Where the same number as mm is way easier to imagine. 172.68.50.99 18:14, 15 January 2025 (UTC)

At first, I was wondering if you would have rather had it in microliters/mm^2, but you meant the column height of the rain, like inches are used in the US. Along the line of L/m^2, something like mL/cm^2 might be nice considering the density of water, although the value also would be different by a factor. SammyChips (talk) 20:51, 15 January 2025 (UTC)

That's the neat thing about the metric system, they are trivially simple to convert. 1l/m² is exactly 1mm. The fact that the meteorology uses the former just stems from the fact that that's how they measure it. The catch the rain on an area of 1m² into a beaker that contains some volume which is measured in liters. What annoys me though, is that noone seems to be talking about how terribly inefficient the fridge in the comic is. Mine only needs a tenth of the one that Whitehat tries to sell, and that's not even particularly good. --21:21, 15 January 2025 (UTC)

UK measurements, once it gets to weather reports/forecasts, tend to be in millimetres (or centimetres, where more for the layperson who don't need mm-resulution; or occasionally recast as 'old money' inches, with really bad rain events summarised in relation to whole feet), which is implicitly the depth to which any area would be filled (in a case where large catchment + funnelling valley situation is concerned, suffering from the run-off, might be reported as "equivalent to N feet of rain", down where the bad effects get concentrated, but this is not a meteorological measure as such).

Not sure I've ever seen volume/area as an end-result figure (might be relevent as an intermediate for measurement/calculation, especially when discussing the funelling effects of the given local geography), but of course it's trivially relatable.

Density of water would only figure in from replacing litres with kilogrammes (litres are 1/1000th of metres³ and any m² is 10,000 times the cm² (or millilitre), so a factor of 10 between L/m² and mL/cm²; divide L to mL by 1000, times m² to cm² by 10,000, => 10x) but I always find it useful to know that three 2L bottles of pop are (very close to, going by the nominal water content alone) 6kg... makes me feel better about lugging the weekly shopping home, where these might be the single most significant part of the weight. More usefully than cross-converting into length-cubed measure. ;) 141.101.98.69 21:42, 15 January 2025 (UTC)

Isn't the point that KwH/day can be simplified to Watts (an average perhaps, but still) 162.158.41.72 (talk) 21:24, 15 January 2025 (please sign your comments with ~~~~)

Yes, the joke seems pretty clearly about watts or kilowatts, not megajoules. Using megajoules doesn't result in any units being canceled; the denominator remains "/day". BatmanAoD (talk) 23:52, 15 January 2025 (UTC)

If the argument for kWh/day is that it's easy for the consumer to understand how it will affect their electricity bill – then kWh/month would be the right choice, because I doubt anyone receives an electricity bill every day. But the salesman prefers 3 kWh/day because it sounds like a smaller number than 90 kWh/month. And of course, if electricity bills were written in joules instead of illogical watt-hours, then MJ/month would be the easiest for the consumer. 162.158.134.90 (talk) 22:31, 15 January 2025 (please sign your comments with ~~~~)

Per-month is tricky. You seem to assume month=30 days, when it can be 28-31 and is only 30 days a third of the time. Per quarter(-year) is a bit more consistent, less fractionally variant and closer to most utility bill frequencies as well, if you're looking for something not as eye-wateringly frightening as an annual estimate (which 'only' varies every 4.1237... years, on average). 172.70.163.47 00:21, 16 January 2025 (UTC)

"Per-month is tricky. You seem to assume month=30 days, when it can be 28-31..." My electric bill for December 2024 is 33 days. The company closes the book when it is convenient, not per some calendar. --PRR (talk) 05:22, 16 January 2025 (UTC)

Which is why electric consumption per month is even more tricky. --Lupo (talk) 06:33, 16 January 2025 (UTC)

It's still per some calendar. Just a calendar of the electric company, that you're not privy to.141.101.98.245 09:36, 16 January 2025 (UTC)

It's an average. We're not talking specifically about February. You could multiply by 365.24/12 and get 91.31 kWh/month on average – but there's only one significant figure in 3 kWh/day. White Hat doesn't say 3.000 kWh/day. You have to round 91.31 to 90 to avoid false precision.

The stated average is an estimate based on assumptions about how much you'll fill the fridge, how often you'll open the door, how long you'll leave the door open, the room temperature in your kitchen, how much surrounding cabinets will restrict air flow across the condenser, et cetera. The combined uncertainties make it meaningless to state a highly precise power consumption. The length of the month is just one of many sources of variation. 162.158.134.90 10:40, 16 January 2025 (UTC)

I suspect this comic is inspired by the much more common pet peeve of incorrect/nonsensical units, frequently encountered in similar contexts. I'm so used to hearing kWh mistakenly written simply as kW, that I initially misread and assumed that's what the comic is about. That's a particularly common example, where you'll hear battery capacities listed in kW, or instantaneous power described in watt-hours. PotatoGod (talk) 09:53, 16 January 2025 (UTC)