Pound-force

The pound-force, or simply pound (abbreviations: lb, lbf, or lbf), is a unit of force. The pound-force is about equal to the gravitational force applied on a mass of one pound on the surface of Earth. Since the 18th century, the unit has been used in low-precision measurements.
In the 20th century, people needed a more precise definition. An official value for acceleration due to gravity was needed. Today, as decided by the General Conference on Weights and Measures, standard gravity is usually taken to be .