As in all fields of measurement, one is free to choose a system of units. The furlong-fortnight-stone system of units may be a convenient system of units for horse racing, but it is inconvenient for scientific measurements. The meter-kilogram-second system of units (M.K.S.) is the system that has been adopted world wide as the international system of units. The United States is one of the few countries that has not committed itself to this system. The rationalized MKS system of units will be used in P142.