It occurs to me that it might be possible to determine a local value of G by observing the tides over a long-ish period. Tide height might be distributed as a normal curve, but it might have a measurable deviance. I wouldn't expect a left/right offset of the X coordinate based on G(local) , but perhaps an asymmetry across the mean X. Seems like a likely candidate for a paper, anyway. Anyone got a pointer to a study/thesis/paper on tides-vs-local-G?