ABSTRACT
There is a profusion of different systems of units in use across the world. Traditional units tended to be defined in terms of a convenient quantity, e.g. a foot (oflength), an atmosphere (of pressure), a knot (of velocity), or a horsepower (of power). To provide a common set of internationally agreed units, the Systerne International d'Unites (or 51 units; see also Chapter 3) was agreed by most countries at a conference in Paris in 1960. However, many units outside this system remain in common use.
