On Wed, 3 Jan 2007, Magnus Danielson wrote: > > Assuming you have corrected for another gravitational field, yes. The > current SI second indirectly assumes a certain gravitational force, we > is assumed to be "at sea level" whatever level that is.

Wrong. The SI second is independent of your reference frame, and is defined according to Einstein's principle of equivalence. What *does* depend on the gravitational potential at the geoid is TAI (and TT), since a timescale (unlike a fundamental unit) is relative to a reference frame. > We still depend on geophysics to some degree. Note that the standard relativistic transformations between TT, TCG, and TCB is (since 2000) independent of the geoid. So although the realization of these timescales is dependent on geophysics (because the atomic clocks they are ultimately based on are sited on the planet) the mathematical models try to avoid it. Tony. -- f.a.n.finch <[EMAIL PROTECTED]> http://dotat.at/ SOLE LUNDY FASTNET IRISH SEA: SOUTHWEST VEERING WEST OR NORTHWEST 7 TO SEVERE GALE 9, LATER DECREASING 4 OR 5. ROUGH OR VERY ROUGH, OCCASIONALLY HIGH IN WEST SOLE. RAIN THEN SCATTERED SHOWERS. MODERATE OR GOOD.