Probably not the best phrase for it, I guess ultimately that just means gravitational field strength, which could be detected by a (very sensitive!) bit of equipment, and the differences in field strength used to infer information about changes in the state of a system.
My specific thinking...
Apologies if these questions have been answered before - I didn't have any luck with google. Something has bugged me for a while about quantum experiments like Schrödinger's cat where a 'black box' system is theorized to be in a superposition of states until observation causes wave function...