# Wikipedia talk:WikiProject Physics/Article titles about multiples and submultiples of units

I'm placing this on a subpage of WP:WikiProject Physics, because apparently there is no such thing as a WP:WikiProject Metrology; I looked on the talk pages of Metre, Kilogram, and Second expecting to find banners of such a project, but I found none, and I guessed WP:PHYS is the closest match. Feel free to move this page to a more appropriate title if it exists.

## What should article titles about multiples and submultiples of units of measurement be?

There is a great inconsistency in article titles about multiples and submultiples of units of measurement, for example:

Why? -- Army1987 – Deeds, not words. 17:49, 4 January 2009 (UTC)

This is an example of when "command-and-control" systems are better than "wisdom of crowd" systems. If only a benign dictator could arise for an hour and make a sweeping judgment about how all these articles should be organized (since there's no obvious way to do it), it would save us lots and lots of work. Ah, well.
Here's my first stab at a suggested organizing principle:
Every basic SI unit should have its own article. All multiple of those units should redirect to those articles, or to individual sections of that article for the particular multiple, with exceptions for very commonly used multiples that have become de-facto units in their own right and deserve an article.(Which should those be?)
Units that are multiples of basic SI units, like kilowatt-hour, should have a single article for the most common usage (whatever that is) with other variations redirecting to that article.
OK, those are pretty obvious. What next, I wonder? - DavidWBrooks (talk) 18:20, 4 January 2009 (UTC)
As for "Which should those be?", gram and centimetre should have their own articles as base units of the CGS. Dunno about other ones... --- Army1987 – Deeds, not words. 18:42, 4 January 2009 (UTC)
I disagree on this point. I think we should have just have a single article for each unit, regardless of magnitude variants. Thus only kilogram and metre articles, which each should mention and link to CGS. I think that will be more useful to the reader. See #Magnitude variants for more on this. —DragonHawk (talk|hist) 19:57, 4 January 2009 (UTC)
Regarding "Why?": Lacking guidance, individual whim and random chance yield inconsistency. Hierarchical control structures have this problem too. Now that someone has pointed out the inconsistency, we can develop a standard and implemented it. Good job on kicking off the discussion! ♦ Regarding "Where?": This is nominally the domain of Wikipedia:Manual of Style. However, we can discuss it here just fine. Whatever we come up with should eventually be folded into WP:MOS somewhere. Perhaps Wikipedia:Naming conventions, perhaps Wikipedia:Manual of Style (dates and numbers)#Units of measurement, perhaps others/multiple. —DragonHawk (talk|hist) 19:41, 4 January 2009 (UTC)

The best reference for SI units is the official SI website. The term they use is base unit. I think millimetre and centimetre should both redirect to metre. Diverting any unit to an order of magnitude is weird. Lightmouse (talk) 18:59, 4 January 2009 (UTC)

• Why? It's not all that difficult to figure out. It is a fairly recent change in Wikipedia software which allows redirects to go to a specific section of an article. Before that, even if you tried to include a section in the redirect link, it wouldn't take you to a specific section of the article as as a link within an article had done for years. Many of the redirects were made long before then; and as you might figure out, changing redirects that do get you to an appropriate article, just to point to a specific section of that article
• So just go fix that.
• This whole discussion is premature. There have been various discussions of some of the issues here in the past; see if you can dig some of them out first. In one particular case, part of the reason for the existence of a separate article is the need to distinguish micrometer from micrometer and the various disputes about what should get primary disambiguation and whatever, and the fact that a discussion of that particular distinction is better dealt with here is a "micrometer" article/redirect/whatever than it is hidden away somewhere in the depths of the meter article. Gene Nygaard (talk) 20:12, 4 January 2009 (UTC)
I think it's worthwhile to have an WP:MOS guideline on this (even if only a few sentences), as that would help alleviate just this sort of confusion. I couldn't find such guidance. That implies that the past discussions never concluded in obvious consensus, or if they did, said consensus wasn't documented. So I don't regard this as "premature". ♦ As far as something like micrometer goes: Why not just redirect micrometre to metre, and expand the dab hatnote at metre to say "For the measurement instrument, see micrometer."? That's what we do for most everything else. —DragonHawk (talk|hist) 20:27, 4 January 2009 (UTC)
Several reasons why not.
• You'd end up with half a screen, maybe even a full screen, full of hatlines, by the time you get micron (disambiguation) and micrometer (device) and everything else at the metre article.
• But if an incoming link is to a specific section, you do not even see those hatlines, unless you move to the top of the page after getting there. Gene Nygaard (talk) 10:12, 5 January 2009 (UTC)

## Magnitude variants

I'm breaking concepts into sections to make discussion earlier to follow.

I generally agree with what has been proposal so far. I'd suggest we "always" merge and redirect magnitude variants of a given unit to one article, regardless of "de facto" status. Even in the case of something like gram, most of the information will and does overlap with kilogram. I'd say we can better serve readers by treating them in the same article; it provides more context, and better informs the reader. We should do this even if it's not an SI unit; the same principle applies. (Note that I'm talking magnitude variants only here; not derived or compound units, like watt (joule/second) or watt-hour.) For things like Centimetre gram second system of units, mention and link to from the normalized main article, again to provide context.

To determine the "base foundation magnitude" to use for the title: Follow standards body guidelines (SI, etc.) when possible. Thus, prefer kilogram over gram. If none can be found, or standards disagree, use the unit(s) without multiple(s). Thus, "foo" instead of "kilofoo".

Magnitude variant redirects should generally go to the main article. There is no need to have a subsection for gigawatt, milliwatt, etc. That is awkward to read. A table with magnitude variants is appropriate. When a variant has popular usage within an industry or field of study, it should be discussed in that context. Thus, a sentence/paragraph/section on how each industry/field uses it, not a sentence/paragraph/section on each unit. —DragonHawk (talk|hist) 19:54, 4 January 2009 (UTC)

I don't understand at all this "If none can be found, or standards disagree" statement. Do you realize that a "base unit" isn't a property of the unit, it isn't a property of an English word. A "base unit" is a term in metrology jargon which applies only when a "system of units" is specified. The SI, a meter-kilogram-second system, has one set of base units. The various centimeter-gram-system systems have different set of base units (including the two obvious ones in its name, centimeters and grams), as well as a distinct set of "derived units" formed by combining those "base units". A meter-ton-kilogram system has another different set of base units. A gravitational foot-pound-second system has a different set of base units than what an absolute foot-pound-second system has. Note also that "base units" doesn't mean the root word to which prefixes are applied; it refers to the building blocks upon which the derived units of that system of measurement are created, by putting together various unitary combinations of the base units. Since this "base unit" terminology doesn't apply to the building blocks for prefixed multiples, it doesn't really have a whole lot to do with how we handle those prefixed multiples. Gene Nygaard (talk) 20:25, 4 January 2009 (UTC)
I didn't write "base unit" but "base magnitude unit", and I quoted it to try and highlight that distinction. We need some kind of concise label for "the magnitude, or lack thereof, we associate with the unit, in the article title and in the main part of the article body". I've struck "base" since that's apparently confusing, and put in "foundation magnitude" as an alternative. Better ideas welcomed.  :) —DragonHawk (talk|hist) 20:35, 4 January 2009 (UTC)
Well, as for kilogram, standards disagree (the kilogram is the "foundation magnitude" in the SI and the gram is the one in the CGS), so "use the unit(s) without multiple(s)", that is "gram". But if there shall be one article, it makes more sense to locate it at kilogram, given that the gram is defined in terms of the kilogram and not the other way round. -- Army1987 – Deeds, not words. 21:26, 4 January 2009 (UTC)
CGS is obsolete. SI is the Universal Standard. End of discussion. Roger (talk) 18:47, 8 January 2009 (UTC)
I wish it were, but I still see stuff such as ${\displaystyle \nabla \cdot \mathbf {E} =4\pi \rho }$ and ${\displaystyle \mathbf {F} =q\mathbf {E} +{\frac {q\mathbf {v} }{c}}\times \mathbf {B} }$ and ${\displaystyle \nabla \times \mathbf {E} =-{\frac {1}{c}}{\frac {\partial \mathbf {B} }{\partial t}}}$ way too often. -- Army1987 – Deeds, not words. 17:50, 9 January 2009 (UTC)

## Unit products

How should we write the names/symbols of units which are products (multiplied) of other units? For example, ampere-hour vs. kilowatt hour. Our options appear to be a space or a hyphen or a middle-dot (·).

WP:UNITS touches on this briefly, but I find it somewhat confusing and perhaps contradictory. Are we supposed to use a middle-dot always, or only for unit symbols, or what? I'll post a note on the talk page there to bring attention to this discussion here.

Beyond WP:MOS, we have the BIPM SI Brochure. §5.2 ¶4 states that unit names should use a space or hyphen. US NIST SP 811 (§9.4) agrees. In §5.1 ¶5, it states that unit symbols should use a space or middle-dot.

I'm not sure if we should standardize on one, or if we should be flexible and allow either. Either way, it might make sense to provide redirects for both variants. Thoughts? —DragonHawk (talk|hist) 20:17, 4 January 2009 (UTC)

No, a middle dot is not an option. That is appropriate for use between symbols for units of measurement. But our article names should be spelled-out words, and a middot is not appropriate there. Gene Nygaard (talk) 20:27, 4 January 2009 (UTC)
Very good point. Unit symbols are outside the scope of this discussion. I've modified the above to reflect. —DragonHawk (talk|hist) 20:43, 4 January 2009 (UTC)
Well, not entirely outside it. We need to deal with sending redirects for unit symbols to various articles or disambiguation pages (e.g. Mm to a disambiguation page because of initial-capitalization-on, Μm to either an article or a specific section of an article). Gene Nygaard (talk) 21:10, 4 January 2009 (UTC)
Huh? What? That one pointed in the only place which was certainly wrong. I've pointed it to MM, which makes much more sense. I think redirecting symbols to units only makes sense when the same combination of letters has no other use. -- Army1987 – Deeds, not words. 21:21, 4 January 2009 (UTC)
No, you are the one who is wrong. That first letter is not an em. So I've moved it back, so you don't get a bunch of links to a disambiguation page on which the proper meaning isn't even so much as mentioned. Gene Nygaard (talk) 22:00, 4 January 2009 (UTC)
Oddly enough, if you click the link for mm (meaning millimetre) you get a disambiguation page which doesn't even link to the article on millimetre. --RexxS (talk) 04:13, 5 January 2009 (UTC)
That's because the first letter of every link is treated as if it were uppercase in Wikipedia. So a link to megameters (Mm) goes to the very same place as a link to millimeters (mm). Furthermore, in this case, all the various capitalizations of MM can be used for links for many other things as well. That's why it goes to a disambiguation page; we cannot tell where the link is intended to go. Gene Nygaard (talk) 10:32, 5 January 2009 (UTC)
Yes, we already knew that. You've missed the point that the disambiguation page (for mm or MM or Mm) doesn't link to the article on millimetre which defeats the object of a dab page. Try clicking on the mm link and getting to millimetre from there. --RexxS (talk) 13:12, 5 January 2009 (UTC)
You are right--I missed that. Good catch! I saw that the symbol was there, not that the unit name wasn't linked. Gene Nygaard (talk) 15:37, 5 January 2009 (UTC)
Fixed. -- Army1987 – Deeds, not words. 15:41, 5 January 2009 (UTC)
Good luck on trying to get any unclarity at Wikipedia:Manual of Style (dates and numbers) changed. What you are likely to end up with is another 500 words of explanation, but no help. Gene Nygaard (talk) 20:30, 4 January 2009 (UTC)
~shrug~ 'Tis the nature of things. I think it's still worth trying. If we don't try, we definitely won't succeed. If I want to admit defeat, I'll just stop coming to Wikpedia.  :) —DragonHawk (talk|hist) 20:43, 4 January 2009 (UTC)

I'd go with "pick either one, and create a redirect from the other one". I think hyphens are more common in the Commonwealth than the US, so, personally, I'd use milliampere-hour for articles written in GB English and milliampere hour for ones in US English, but I think prescribing that would be instruction creep. -- Army1987 – Deeds, not words. 21:41, 4 January 2009 (UTC)

I agree; though I'd say just the opposite as to where one form is more common than the other. In any case, the usage is too mixed in any geographical area for it to be a national varieties of English issue. Just make sure the redirects exist. Gene Nygaard (talk) 22:11, 4 January 2009 (UTC)

Matter of fact, the current version of MOS:NUM says:

When unit names are combined by multiplication, separate them with a hyphen. A kilogram-calorie (kg·cal) is not the same thing as a kilogram calorie (kcal). Pluralization is achieved by adding an s at the end (e.g., write A force of ten newton-metres). [Formatting removed by copy&paste, won't bother to reproduce it]

Instruction creep justified by implausible example. I can't think of any quantity which is dimensionally the product of a mass by an energy, and if there's one it'd probably not be expressed in kg·cal but in kg·J. -- Army1987 – Deeds, not words. 01:07, 5 January 2009 (UTC)

It is indeed the worst example possible. I can't believe that kg·cal could represent anything. A 'kilogram calorie' (or 'kilogram-calorie') is just an antiquated name for kilocalorie and to use that as an example of "When unit names are combined by multiplication" looks most like an April Fool's joke to me. --RexxS (talk) 04:13, 5 January 2009 (UTC)
Quite the contrary. "Kilocalorie" is just a convoluted name for the "calorie"—the kilogram calorie is the only calorie still in use today. We don't need to worry much about any historical use of the small calorie by chemists and physicists, which they abandoned ages ago. Better just to abandon that nonsense, and never use "kilocalorie" since nobody ever used the prefix "kilo-" with the large calorie which is the one still in general use today. Gene Nygaard (talk) 10:17, 5 January 2009 (UTC)
But now that I've gotten that out of the way, I agree with Army1987's observation that the MoS is way out of whack, and that there is no real ambiguity in what "kilogram calorie" means even if someone hyphenates it. Far more appropriate and likely to be found useful would be a warning not to use "kg cal" or "kg·cal" as a symbol for the "kilogram calorie", but that isn't what the MoS was dealing with. Gene Nygaard (talk) 10:28, 5 January 2009 (UTC)
"Quite the contrary" to what? I linked kilocalorie so you could see what Wikipedia says about the calorie (an ambiguous unit that I'd prefer not to use). I suggest you read the article and note that kilogram calorie also links there. The phrase "kilogram-calorie" is used in the lead, so it would seem that our own editors already understand that "kilogram calorie" and "kilogram-calorie" are indeed the same thing. That's why the quoted part of MOS:NUM is (1) wrong in its assumption that they are different and (2) creates unhelpful guidance, based on a misunderstanding that "kilogram calorie" and its synonyms are examples of "combining units by multiplication".
As for the dismissive advice, never use "kilocalorie" since nobody ever used the prefix "kilo-" with the large calorie which is the one still in general use today - it gets 253,000 ghits, which is a lot of "nobodies". Am I right to assume you would prefer everyone to use "calorie" (despite the well-documented potential for ambiguity)? --RexxS (talk) 13:12, 5 January 2009 (UTC)

Actually, the point of the MoS is that kilogram calorie is not a product of units and so it shouldn't be written kilogram-calorie (note that these are two links) as if it were one. It is still wrong because 1) the product of units is often spelled with a hyphen, too; 2) the kcal is often spelled with a space, too. I'd just write "kilocalorie". As for your ghits, they likely refer to the kilocalorie of 1000 gram calories, not 1000 kilogram calories, i.e. they use "kilo-" with the small calorie, and a small kilocalorie is the same as a large calorie. Gene's point is that no-one uses the large kilocalorie (1,000,000 small calories), I guess. -- Army1987 – Deeds, not words. 14:05, 5 January 2009 (UTC)
Yes, that's what I had in mind—nobody uses kilo- as a prefix to the large calorie; which is, of course, the original calorie, older than the small calorie, or gram calorie. Lots of people seem to have gotten the erroneous impression that using calories in the dietary sense results from dropping the prefix kilo- from what was originally kilocalories. That is flat-out false.
So what we have today is that "calorie" usually means the very same thing as "kilocalorie". But it ends up that many people pretend to be using small calories, in a context where large calories are normally used, because the prefixed version ends up being less ambiguous that the unprefixed one. It is still highly confusing to do so, however. In fact, in many places such as in the UK, the word is generally written out as calories, but if a symbols is used, it is written "kcal". True to a lesser extent in the U.S. as well, except that "kcal" is only likely to appear in scientific journals, not on the labels of food and discussions of diets. Gene Nygaard (talk) 15:54, 5 January 2009 (UTC)
I think we all agree. Is there any chance we could get consensus to revise that line in MoS now? --RexxS (talk) 19:25, 5 January 2009 (UTC)
Try putting an {{editprotected}} tag on WT:MOSNUM, pointing to this discussion. -- Army1987 – Deeds, not words. 03:28, 6 January 2009 (UTC)
FWIW, the product of a mass by an energy is a squared momentum, and in that case it would just be measured in the square of a unit of momentum. (This both by trying to mentally determine how kg2 m2/s2 could be factored, and by trying to remember formulas with ${\displaystyle mE}$ in them.) Anyway, if there really is a "foo bar" unit which has a snowball's chance in hell of being ever confused with the product of one foo by one bar, I will put a {{editprotected}} tag on WT:MOSNUM asking to replace the example. But I strongly suspect that no such thing exists. -- Army1987 – Deeds, not words. 13:07, 5 January 2009 (UTC)
It isn't edit protected now, so fix it. And if you get into an edit war over it, have somebody edit-protect it again. Gene Nygaard (talk) 06:24, 6 January 2009 (UTC)
What are you referring to? Wikipedia:Manual of Style (dates and numbers) is still protected. (It has been indefinitely protected by Woody since 20 November.) -- Army1987 – Deeds, not words. 14:35, 6 January 2009 (UTC)