The Mean Aerodynamic Chord (MAC) is the average distance from the leading edge to the trailing edge of the wing. LEMAC is the Leading Edge of the MAC. Typically, in large aircraft, the acceptable Weight and Balance range is expressed as a percentage of MAC (%MAC). In order for the aircraft to be safely controllable, the C-of-G (Centre of Gravity, CG) must be within a certain percentages of MAC. %MAC, that is CG as a percentage of MAC, is given in the equation above.