A non-decimal British system of units based on the foot, pound, and second, formerly used in engineering. It also uses the thermodynamic Rankine scale (°R) for temperature. The gravitational unit of force is called the pound force (lb_f) and is defined as the standard gravitational field that exerts a force of one pound on a mass of one avoirdupois pound. The standard gravitational acceleration (g) is 32.174 ft s^-2. The system has now been replaced by SI units.