In the unit force-mass foot-pound-second system, the base unit of length (equivalently, of distance) is the foot, and the base unit of time is the second. The name pound is applied to both the unit of mass and the unit of force (equivalently, of weight), though, since these are in fact different quantities, it would be better to refer to two separate units, the pound-mass and the pound-force, as base units of the unit force-mass foot-pound-second system.