|A point near the centre of the aeroplane. It moves longitudinally as masses are added forward and aft of its location.
|The point through which the sum of the mass values (of the aeroplane and its contents) is assumed to act vertically.
|A variable point, that is dependent on the load distribution for its location, from which all balance arms are measured
|A fixed point from which all balance arms are measured. It may be located anywhere on the aeroplane's longitudinal axis or on the extensions to that axis.