Aircraft are weighed either on a weigh bridge or more commonly with a load cell at each jacking point. With the aircraft on the load cells, the masses measured by each cell are then entered into the schedule. The moments are calculated and the Basic Empty Mass and Centre of Gravity position are then declared on the schedule.

Basic Empty Mass (BEM) is the mass of an aircraft plus standard items such as: unusable fuel and other unusable fluids; lubricating oil in engine and auxiliary units; fire extinguishers; pyrotechnics; emergency oxygen equipment; supplementary electronic equipment.

Thus, when preparing to carry out the weighing procedure on an aircraft all useable fuel must be drained, since only unusable fuel is included.