> > (hmm. wouldn't it have been nice if the meter had been picked so that
> > 1g==10m/s^2 instead of that "tiny fraction of long distance" thing?)
>
> The "tiny fraction of long distance" is long past; now it's based on the
> speed of light and a time AFAIK. Basing it on the gravity acceleration of
> the Earth would be a bit problematic, I think, as this is probably not
even
> in a well-defined place as constant as they want the meter to be. I'm not
> sure, but probably the tidal movement alone already creates a disturbance
> in the gravity acceleration that's above the precision they use for the
> meter.
>

I _am_ sure :-)

Not so much tidal movement, but that which causes tidal movement. The
relative movements of the sun/moon and other planets can cause nearly 1%
variation in local 'g' over time. I don't have the numbers handy, but there
is also a significant variation dependant upon altitude. So much that
high-end 'g' meters can discern a few meters of altitude difference. Others
may weigh in here with more details but local gravity variations have long
been used as a tool for subterranean geological surveyors, like those used
to find oil.

-Denny

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