Re: Measurements revisited

On Wed, 14 Oct 1998 12:22:32 -0400, John Cowan <cowan@...>
wrote:

>Nik Taylor wrote:
>
>> > Distance makes more sense to me as a basic unit rather than deriving=
 it
>> > from speed and time, because of the relative ease of measuring =
distance.
>
>Actually not.  We can measure time far more precisely now, and so
>the meter was redefined in 1983 thus:
>
>        The metre is the length of the path travelled by light in
>        vacuum during a time interval of 1/299792458 of a
>        second.
>
>A consequence is that the speed of light is now a defined, not a
>measured, quantity!
Well, ease and precision aren't the same thing, of course. But you have a
good point. If the goal of the measuring system is precision, which
physical constants should be the basis of the units? The speed of light =
is
very precisely known (even by the old definitions of the units). I used =
the
speed of light, the rest mass of the electron, and Planck's constant to
arrive at my basic Jarrda unit of length (h-bar / me c * 8^13, or about
21.23 cm), but there might be a better alternative that gives more =
precise
units.