measuring gravity

Had a planned power outage over the weekend and one of the computers didn't come up again and needed some prodding. The computer is used to log gravity measured by one gravity meters in today's blip. The most obvious variation of gravity are the tides. Gravity measurements can also be used to get an idea of what is in the subsurface. Measuring gravity is actually quite difficult. Anyway,  if are curious you can see what is being logged here.