Water displacement is used to find the volume of irregular solids as discovered by Archimedes
He discovered that you have to find the volume, mass, and density of something
He discovered the method to calculate the volume of a irregular object (rock).
Archimedes discovered that all substances have a unique density - the amount of mass contained in a fixed volume of the substance.
Archimedes discovered volume displacement when he was in the bath tub because the weight of an object makes the water rise.But the volume of the water was constant.He then ran outside on the streets screaming,EUREKA!...naked
How? With his brain! That's how he answered it
measure and calculate or find displacement with Archimedes principal
apply Archimedes principle