This is idiotic. The mountains are on tectonic plates, that float on a molten inner earth. So do the mean relative to the other floating plates or surrounding areas of the same plate? Or do they mean the ocean level that constantly rises and falls? And the ocean that is literally never stable being driven by wind, currents, and even the pull of the moon each day.
And they notices an inch of difference?
I call BS. Their level of precision exceeds your ability to measure. Pure BS.
Ever wonder how all those monoliths remain accurately aligned with the stars, since the plates are always moving?