How can you figure out whether the Glass Is half full ?

Question

You are in an empty room with a transparent glass of water.
The glass is a right cylinder and appears to be half full.
How can you accurately figure out whether the glass is half full,
more than half full, or less than half full?
You have no rulers or writing utensils.

Answer 1

Tip the glass of water until the water reaches the rim of the glass and if the water lines up perfectly with the bottom rim of the glass, it is half full.