What exactly is "exact" (was Clean Singleton Docstrings)

Marko Rauhamaa marko at pacujo.net
Mon Jul 18 11:40:10 EDT 2016


Ian Kelly <ian.g.kelly at gmail.com>:

> Off-topic, c being a fundamental constant is actually in the latter
> category. Its *exact* value is 299792458 m/s.
>
> The length of the meter, on the other hand, is defined as the distance
> traveled by light in a vacuum in 1/299792458 seconds and is subject to
> the precision of measurements.

Since both c and the second are exact magnitudes, so is the meter.

   The second [...] is quantitatively defined in terms of exactly
   9,192,631,770 periods of a certain frequency of radiation from the
   caesium atom: a so-called atomic clock.
   <URL: https://en.wikipedia.org/wiki/Second>


Marko



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