"... during the past 20–30 years, the subject of has—as a result of advances in measurement technologies—been transformed from a chiefly theoretical endeavor that explored beautiful theorems, involving the and equations, to an experimental science—a science that has come of age as one can now make real-time measurements at the levels at which geophysical happenings are taking place. And absolute gravimetry (along with very long baseline interferometry, global positioning satellites, satellite ranging, etc.) was and is contributing to this revolution."