This is an archive of past discussions about International System of Units. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page.
The ISQ does not define units. The ISO 80000 series does, but it makes a clear distinction in the introduction, e.g.[1]
In parts 3 to 14 of this International Standard, the quantities and relations among them, which are a subset of the ISQ, are given on the left-hand pages, and the units of the SI (and some other units) are given on the right-hand pages. Some additional quantities and units are also given on the left-hand and right-hand pages, respectively.
The ISQ does not comprise all of the extensive lists of quantities in the ISO 80000 series, which as mentioned in the above quote includes additional quantities. That introduction also states
ISQ is a shorthand notation for the “system of quantities on which the SI is based”, which was the phrase used for this system in ISO 31.
In the ISO and IEC 80000 series the quantities and equations used with the SI are known as the International System of Quantities
Far from describing the entire contents of that series as the ISQ, it's explicitly restrictive.
I think this means we have to edit some recent additions, either to make it clear that some of the units mentioned are not part of SI or the ISQ, or to simply remove them as out of scope. What do others think? NebY (talk) 14:29, 17 May 2015 (UTC)
The SI and ISQ are 2 different things, and nearly everything that can be written about the ISQ is out of scope. In my opinion the ISQ material should never have been brought into the SI article. Dondervogel 2 (talk) 16:00, 17 May 2015 (UTC)
NebY seems to be making a valid point about ISQ and units. ISQ is in scope inasmuch as it defines the quantities for which SI defines units, the distinction between quantities and units should be made clear, and I believe SI references the ISQ. I'm not disagreeing with Dondervogel, but if the units are not defined by ISQ itself, the most that should be said in this article under ISQ about specific units is that ISO 80000 defines many additional units. I was not involved in the merge, but it the ISQ seems to have the "feel" of needing it is own article, even though before the merge it was only a stub. —Quondum16:30, 17 May 2015 (UTC)
Done I've undone the redirect of International System of Quantities, removed material here relating to quantities that are outside the ISQ and units that are outside the ISQ and SI, and removed the expansion-needed tag as there's no clear need for any more to be said about the ISQ in this article. I'm not sure there is much more to be said about the ISQ anyway. NebY (talk) 17:22, 18 May 2015 (UTC)
Thank you. This is a better starting point. The edits I made are still relevant to the ISQ article so I have reinstated them there. If there are still concerns about my interpretation of the cited references (and I see no reason for such concerns to have dissipated), they are best raised at the ISQ Talk page. Dondervogel 2 (talk) 17:44, 18 May 2015 (UTC)
Top image confusion
Latest comment: 9 years ago32 comments3 people in discussion
Currently we have top image Image:SI base unit.svg, that shows the seven quantities and also their inter-dependencies (arrows). I think the arrows are not needed in here, and cause confusion given that this is the top image.
The main information is that these seven are independent, e.g. a temperature can not be derived from the other units. Of course the arrows are correct, in that "ampere is defined partially in metre", but that partial dependency is confusing the concept of independency.
The arrows are most useful in explaining the base definitions, but that should be in a section only. It must have context stressing the partial part. I propose to move this inage to that section or paragraph below, and top create a new image by removing the arrows (to improve clarity, we could add words like "A - electric current"). -DePiep (talk) 11:47, 16 May 2015 (UTC)
This proposal seems to confuse quantities with units, and dependency with derivation.
The seven base quantities of the ISQ (such as length and electrical current) are independent. Their symbols are L, M, T, I, Θ, N and J. The top image is not a chart of the base quantities.
The seven base units of SI (such as metre and ampere) are largely interdependent. Their symbols are m, kg, s, A, K, mol and cd. The image charts their interdependencies.
There are also twenty-two named derived units such as the newton and the pascal, but this image charts dependency, not derivation.
We could have a further image in the International System of Units#International System of Quantities section that - much as proposed - simply showed the seven quantities as seven coloured circles. I'm not sure how much such an image would communicate, except perhaps as a contrast to the chart of unit interdependencies. I don't think such an image of quantities would serve as the main image of this article about units. NebY (talk) 13:03, 16 May 2015 (UTC)
I stand corrected with the better descriptions NebY added. I think it does not change the gist of my proposal. Where I wrote "partially dependent" NebY writes "largely interdependent". The essence of the seven units is that they can not be expressed in the others, and that is what should be shown. The arrows in the graph stress the unimportant point, and so obscures the main point. NebY says "I'm not sure how much such an image would communicate" implies we do not need to list these units at all, and that the arrows are the main information to convey, in this article? I think this is upside down. To improve the communication, we could add the quantity names to the circles (icons would be good too, but are difficult to think of because it's abstracts). -DePiep (talk) 13:41, 16 May 2015 (UTC)
It took a little thinking, but I think DePiep has a point. The chart does not, IMO, belong with the lead, and as a chart it chooses to emphasize only part of the dependency picture, and is thus incomplete and confusing w.r.t. what it tries to express. What is missing is what each unit depends on, in terms of physical measurements (periods of some radiation, speed of light, the prototype kilogram, etc.), as well as the further dependencies of the derived units. The metre could just as easily be defined in terms of wavelengths of the same radiation, and the second in terms of metre and the speed of light (or still kept in terms of periods). The dependencies between the definitions are thus entirely arbitrary, determined by convenience of definition only. What distinguishes the derived units is the absence of direct dependence of their definition on any physical measurements, but this distinction is still rather arbitrary (and inconsistent: the candela does not depend on any additional physical measurement, only on a standardized function). I think there is little to be gained from this diagram, though it could be replaced by an expanded version showing all the units and what their definition depends on. —Quondum18:02, 16 May 2015 (UTC)
I do agree that the current image doesn't serve well as an introductory one. Since DePiep raised the question, I've been wondering whether there's a case that the interdependencies illustrate the coherence of the system but coming to the same broad conclusion as Quondum. It's a little harsh to call, say, the choice of a one-metre separation in the definition of the ampere "arbitrary", but yes, it's merely convenient and does nothing to integrate the ampere into the system. I'd be happy to see the image removed or possibly moved to another section, perhaps to join the other image in International System of Units#Redefinition of units, and I don't think we need to wait until we've found or made a replacement. NebY (talk) 13:45, 17 May 2015 (UTC)
Sounds good. That "other image" is nice because it incorporates the additional physical dependencies, which at a minimum should be included in the one we're talking about. —Quondum14:57, 17 May 2015 (UTC)
I've moved it into the suggested section, where it serves now as a point of comparison for the other one. —Quondum16:51, 17 May 2015 (UTC)
I object to the removal of the image from the top. It should be replaced. It was not wrong, it just needed improvement (proposal is an other, new image). -DePiep (talk) 19:17, 17 May 2015 (UTC)
You have proposed an image in the lead pictorially communicating only a list of base units, possibly with the names of the associated quantities. I do not object to this proposal, but I do not see the current (unmodified) image as belonging in the lead. —Quondum20:30, 17 May 2015 (UTC)
Yes that I know because you removed the image. My proposal is to replace it with a similar image without the arrows. Since you agreed, you should wait for that alternative. Going solo is not an outcome here. -DePiep (talk) 20:59, 17 May 2015 (UTC)
That is putting it a bit strongly. I did not remove the image, but moved it lower down in the article. This was with the support of the only other editor on this thread, so it should not be called going solo. —Quondum22:09, 17 May 2015 (UTC)
You could have waited for DePiep's opinion, which might have been persuasive. When I said "I'd be happy", I wasn't calling for instant action before anyone else had a chance to express an opinion. NebY (talk) 17:09, 18 May 2015 (UTC)
Aside from the omission of the dependencies of the base units on other things (primarily physical measurements), I note one inaccuracy the the diagram: the current definition of the ampere (a base unit) depends on the definition of a derived unit, the newton. Without showing this dependency, the diagram is inconsistent. (I know that one can "skip" an intermediary definition in principle, but if one allows that, the whole structure and point of the diagram becomes moot.) —Quondum 16:51, 17 May 2015 (UTC
Isn't that just the difference between derivation and dependency again? Yes, the ampere is defined in terms of newtons and metres, but the whole point of the derived units is that they can be expressed entirely in terms of the base units and so they have exactly the same dependencies as their base units. Basically, they're a very convenient shorthand. The ampere remains dependent on the definitions of the kilogram, metre and second; changes in the value of the kilogram affect the value of the ampere. (BTW, the term "moot" is tricky in transatlantic conversations. In American English, a moot point is irrelevant but in British English it's an unaddressed key question, the elephant in the room. It's like the problem with "tabling" a question.) NebY (talk) 17:36, 17 May 2015 (UTC)
Yes, it is helpful to distinguish which of derivation and dependency one is meaning. Derivation is agnostic to intermediary definitions. One can say that the ampere is derived from the prototype kilogram, a given period, the speed of light, and the measurement of a force due to a current. IMO, it would not be correct to say that one unit is derived from a definition of another unit. I think my comments about the inconsistency of the diagram still stand (applied to interdependencies of definitions), and it communicating nonsense (applied to dependencies in derivation). Thanks for the useful data point on "moot" – I was only aware of what you describe as the British English meaning. —Quondum18:41, 17 May 2015 (UTC)
On this aspect of dependency, I disagree strongly. The ampere is dependent on the metre, kilogram and second. NebY (talk) 17:09, 18 May 2015 (UTC)
You seem to be confusing dependency on a definition and dependency on the value of a unit. For example, if I define x=yz and w=x/y, is w dependent on y? Its definition depends on the definition of y, but w does not depend on y. But isn't this irrelevant anyway? We need to decide what the diagram is to represent; until we can clearly formulate what the diagram is to depict, debating individual arrows is silly. —Quondum17:50, 18 May 2015 (UTC)
This is deviating into a expose about derivation and dependency (very interesting and instructive to me). But, my core point is that e.g. ampere is only partially defined using length and time. It also has the "essential ampere" thing (electric current) that gives it its rightful place in the set of seven. IMO, the arrows are stressing that length, mass and time presence (in itself not wrong of course), distracting from this.For a better illustration, I suggest (again omitting exact correctness) that the unit "A" can have the name "ampere" and even the quantity "electric current" mentioned. This image is also used in generic template {{SI units}}. -DePiep (talk) 18:41, 18 May 2015 (UTC)
An image for the lead that shows the base unit symbols, their names, and the quantities they measure seems good to me. Your comment about partial definitions applies to every unit and the associated arrows. Are you proposing removing all the arrows? (I would agree with that, if you are.) Also I agree that your observation applies to the image in the template, and the proposed image would be a good candidate for use there too. —Quondum20:11, 18 May 2015 (UTC)
Yes I propose to create a new image, that has all arrows removed [STEP 1]. That is the better image for the template too. The existing image can be used in specialized sections like today's #Redefinition of units section.
[STEP 2] Later in the design, we can add more information for every unit to that new image. Takes graphic design, for example because it is small in the template. To illustrate the seven units/quantities. I think to the Reader, this unit-vs-quantity distinction is minor compared to the grand independency. -DePiep (talk) 20:40, 18 May 2015 (UTC)
IMO, the new image (Step 1) is suitable for the lead of this article and for the template (I think it is an improvement on the previous one for both contexts: lead and template). Step 2 also sounds good, for when someone with the means can do it.
re 'rearrange': good idea. Sorry I don't have time for this - breaking my promise then. CAn you use this new image? -DePiep (talk) 21:09, 22 May 2015 (UTC)
Sorry I've been away so long. I do think the article looks better with an image there. I'll admit to finding this one doesn't say much at all - but I can't think of anything better right now. Sorry! NebY (talk) 21:47, 22 May 2015 (UTC)
It works for me. It is a good basis for considering what might be worth communicating with the image. I've also used it to replace the image in the {{SI units}}. If I knew how edit the image, I might tackle implementing suggestions, but anyone else can implement these if they choose to. —Quondum21:50, 22 May 2015 (UTC)
Wouldn't it be more instructive too have in the circle, for example: "Ampere" (the "A" could be omitted!, but will be there too. Also, the circle could say "electric current" for the physical quantity. -DePiep (talk) 21:58, 23 May 2015 (UTC)
I'm not too sure. I'd prefer to see units (A or ampere) than quantities (electric current) in the circle; the quantity is not what the article is about, so that could be next to the circle as a sort of note. I see little difference between the unit name (ampere) and unit symbol (A), though. —Quondum23:27, 23 May 2015 (UTC)
Done I've undone the redirect of International System of Quantities, removed material here relating to quantities that are outside the ISQ and units that are outside the ISQ and SI, and removed the expansion-needed tag as there's no clear need for any more to be said about the ISQ in this article. I'm not sure there is much more to be said about the ISQ anyway. NebY (talk) 17:22, 18 May 2015 (UTC)
