 The top platen can then be mechanically driven up or down along the axis of the cylinder to squeeze the material.The distance that the upper platen travels is measured as a function of the force required to move it, as the pressure of the surrounding water is carefully controlled.The net change in volume of the material can also be measured by how much water moves in or out of the surrounding bath, but is typically measured - when the sample is saturated with water - by measuring the amount of water that flows into or out of the sample's pores.