Half a Glass of Water

Suppose you're naked in a bare room with nothing but a glass of water. The glass is a right cylinder and seems to be about half-full. But, because you have NOTHING else to do (given that you're naked in a bare room...not the most exciting place in the world) you want to know if the glass is more than half-full, exactly half-full, or less than half-full. What do you do?