The ullage method refers to the measurement of the distance (i.e., the space) between the liquid’s surface and the top of the inner surface of a tank. Ullage tables are located on the ships. These tables are produced in relation to a tank’s interior volume as measured from a reference point. The sounding method is the opposite of the Ullage method. This approach involves measuring the distance between various reference points at the tank’s bottom and the liquid’s surface to determine the depth of a tank of liquid.