Do they have testing equipment that can determine the pressure in an already inflated ball, without having to release some of the air to get that data? Something like a Rockwell hardness test for inflatable balls, for instance? Or does it come down to what it feels like to a game official (pressing a thumb into the ball would be a sort of Rockwell hardness test; but it’s obviously not very reliable)?
A scale? It measures the total weight of the ball and enclosed air. Pressure may change, but the number of molecules inside the ball does not.