On Wed, 14 Oct 1998 12:22:32 -0400, John Cowan <[log in to unmask]> 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.