Talk:International System of Units/Archives/01/2015

Why is the table 'Named units derived from SI base units' based on a NIST recommendation?
The table should be based on Table 3 in the SI Brochure Ed.8 2006 (not some interpretation thereof) and its amendments in the BIPM SI Supplement 2014 (http://www.bipm.org/utils/common/pdf/si_supplement_2014.pdf). In particular, the 'quantity' column should be placed first, and renamed 'Derived quantity', to reflect the primacy of 'quantity'. Objections, anyone? Adamtester (talk) 01:40, 3 January 2015 (UTC)
 * The link did not work as given - I hope you don't mind me editing it. Basically, I agree that the table here should be driven by a BIPM publication and not by NIST's interpretation. Dondervogel 2 (talk) 15:33, 4 January 2015 (UTC)
 * The NIST document seems to be a good reliable source and rather less of a primary source than the SI Brochure. In any case, the ordering of columns is an editorial decision, independent of the sources used. The table is currently consistent with the one above in International System of Units and I think a little more accessible to the lay reader, who may not think principally in terms of formal quantity and even be more familiar with the difference between, say, watt and joule than that between power and energy. NebY (talk) 16:29, 4 January 2015 (UTC)
 * It's a very good point that the derived units table is currently consistent with the base units one. So it should remain; however, this would just make it a question of what to do with both.  One might dispute the applicability of WP:PRIMARY in settling the BIPM vs NIST question in general but I would agree that with respect to this issue it's completely irrelevant in that this is, as NebY notes, an issue not of what information to present but of how to present it, which is an editorial consideration.  So, forget the order of columns suggested by this and that source and let's look at the actual issue: the primacy of quantity verses accessibility to the reader.  These are both good points, I'd tend to lean more towards the latter, though, since our purpose being to deliver information, comprehensibility would generally have to trump strict adherence to logical structure (just my tuppence worth). Jimp 03:20, 5 January 2015 (UTC)

Thank you all for thoughtful polite responses. I think on balance I'll let accessibility for a lay reader trump primary source. I'll let it be. Adamtester (talk) 11:26, 8 January 2015 (UTC)

BIPM revision of base units
Is there a BIPM initiative to demote the candela and ampere from the status of base units to subsidiary units? This article makes it clear that the candela is in terms of base units for the basic quantities of distance, mass, and time. Likewise, the ampere is in terms of base units for the base quantities of distance, mass, and time. In other words, the "building blocks" of the candela and ampere are other BIPM base units.

The mole, too, looks like a candidate for demotion to subsidiary status given its definition in terms of kilograms. This would leave just four base units in BIPM's system, and these are defined in terms of four basic quantities. And if time and distance are generalized correctly with the concept of interval, should not also the second and the meter be demoted to subsidiary status in favor of a new base unit for interval? Then there'd be just three base units defined in terms of three basic quantities: mass, interval, and temperature.

It's unfortunate that this article doesn't help the reader very much to distinguish the concept of base unit from basic quantity, though perhaps it's not the right place to do so. Yet International System of Quantities, too, isn't particularly helpful, for ISQ is defined in terms of a "style guide" called ISO/IEC 80000.

12.175.62.2 (talk) 16:59, 14 January 2015 (UTC)


 * Making those units derived instead of base units would break the principle of "coherence" in the system. In a coherent system of units, derived units are created by multiplying and dividing base units, but no other factors are allowed other than 1. Since those units you listed contain conversion factors other than 1 in their definitions, they cannot be derived units in a coherent system. Therefore they have to be defined as base units. Indefatigable (talk) 17:34, 15 January 2015 (UTC)