The details of the entire procedure are given in the ASTM D924 standard and are only briefly mentioned here. The measurements are made in specially designed cells that are machined to precise dimensions. The measurements are done at precise temperature, usually 25℃ and 100℃, thus the cells have to kept at a constant temperature. The actual measurement is one of comparing the capacitance of the cell filled with the insulating fluid sample in a sensitive electronic bridge circuit. The result is usually expressed as a percentage for the dissipation factor or power factor.