Talk:International System of Units/Archives/08/2019

What update is being requested?

@Koavf: Could you please clarify what you are asking for with this 'update section' template? It is not clear to me that it is not up to date in any particular respect. —Quondum 13:14, 2 July 2019 (UTC)

Quondum, We need the 2019 definitions. Now, the table has definitions from the 1960s. ―Justin (koavf)❤T☮C☺M☯ 15:30, 2 July 2019 (UTC)

Koavf, it already has the revised definitions, along with their historical versions. It sounds like you are suggesting a restructure, not an update: moving the history into a history section, leaving behind only the current (2019) definitions. I would agree with such a change, but in the interim, the hatnote does not communicate this idea. There is an aspect that is not quite up to date: the status of the base units has changed (they no longer form the basis of the definition of the SI; they have been supplanted by the seven constants in this regard). But capturing this is more subtle and needs thought. —Quondum 15:48, 2 July 2019 (UTC)

They never formed the basis of the definitions for SI, because the ampere was defined in terms of length and force. But they are used as the units to define (in a mathematical, not operational sense) derived units with special names. Jc3s5h (talk) 16:29, 2 July 2019 (UTC)

Quondum, It says "current" but it's not current. ―Justin (koavf)❤T☮C☺M☯ 16:41, 2 July 2019 (UTC)

Jc3s5h, whatever the exact characterization, there seems to have been a deliberate change of emphasis, which we may choose to include; this is not particularly important though.

Koavf, I see four "current" definitions tagged 2019, which I assume you consider current. I see three more tagged with earlier dates because that is when these definitions were originally adopted. However, these have effectively remained unchanged, and are thus current. All of the "current" definitions are effectively paraphrases of the 2019 definitions, and are consequently current. If you disagree, you'll have to be more specific. —Quondum 17:22, 2 July 2019 (UTC)

Quondum, Okay. Maybe I'm just sloppy. ―Justin (koavf)❤T☮C☺M☯ 17:47, 2 July 2019 (UTC)

I think the whole lede, at least, needs to be updated. I will try to do this incrementally, because a "big bang" approach does not allow for comments by others. We need to move some stuff to the historical section, and we need to make it clear that the entire SI is now defined in terms of seven exactly-defined "arbitrary" numbers chosen to make the values of the base units equal (to the limits of current metrology) to the values that were measured based on the older definitions. It is no longer possible to "measure the speed of light". One can only measure the value provided by an experiment and compare it to the definition of the speed of light. -Arch dude (talk) 19:06, 16 August 2019 (UTC)

There is room for improvement in the lead, yes, so by all means, do so. On the statement that it is no longer possible to measure the speed of light, as an isolated statement this does not really make sense. One can still measure it in terms of a realization of SI units, but what that would serve to do is to check accuracy of the measurement process. It would be true to say that it is not possible to refine the numeric value of the speed of light in SI units because it has a defined value. Also, one should not really say that the "entire SI" in now defined in terms of constants, because there are many other aspects to the SI than only its base units, including a strong dependence on the International System of Quantities. —Quondum 20:26, 16 August 2019 (UTC)

Road signs

This insertion of road signs by User:DeFacto seems to be outside the scope of the article, which is about what the SI is, not about its specific applications. I think the added material would be better omitted or moved into a more specific article. —Quondum 19:18, 7 October 2018 (UTC)

I agree. I removed the section. --IngenieroLoco (talk) 20:12, 21 August 2019 (UTC)