Re: Metric Time (was Re: Why not 13 months? (Was La Systeme Metrique))

Wouter den Otter (
11 Oct 1995 07:36:00 GMT (Dik T. Winter) writes:

>In article <> writes:
> > The metre, however, is a contrived unit of length - an abstract
> > concept, which is DEFININED very, very precisely. You may 'know
> > the metre to a very high precision', but that knowledge is the
> > definition...

>You are wrong. The definition of the metre is exact (mumble mumble times
>the distance light travels in a vacuum mumble mumble in one second). As
>the speed of light is only known to a high precision the actual value of
>the metre is also only known to a high precision; but its definition is
>exact. (Of course the definition can change as it has done at least two
>times.) If the definition was only very precise the definition would
>contain the word "about" at least once.

Some kind of contradiction here:
How do you measure the speed of light, if you don't
have a unit of length that is independent of that speed?

In SI the speed of light itself is defined. Combining with the defined
unit of time then yields the defined unit of length.