[4] Units for other physical quantities are derived from this set as needed.
In English Engineering Units, the pound-mass and the pound-force are distinct base units, and Newton's Second Law of Motion takes the form
The term English units strictly refers to the system used in England until 1826, when it was replaced by (more rigorously defined) Imperial units.
A similar system, termed British Engineering Units by Halliday and Resnick (1974), is a system that uses the slug as the unit of mass, and in which Newton's law retains the form F = ma.
[5] Modern British engineering practice has used SI base units since at least the late 1970s.