A 30 cm daily vertical offset is pretty typical. I've seen over 45 cm. Horizontal offsets are usually less than +/- 75 mm per day with the longitude displacement typically twice the latitude displacement. Heather uses a standard model (see http://geodesyworld.github.io/SOFTS/solid.htm) to calculate earth tides. I converted the Fortran code to C and use a more accurate routine for calculating sun and moon positions. The gravity calculation code is from TVB's code. Actual tides experienced at a given location depend can depend upon locally unique factors like underground geology and nearby bodies of water. Compensating altitude for an optical clock would be considerably more complex. ------------------- > You're place really moved a foot in 48 hours? Impressive and scary!