Each system
of measures is based on a basic unit from which the others are formed
as simple fractions or multiples.

For example, the basic unit of
length in metric system is the metre, and this is divided into 100
equal parts to give a centimeter or 1000 equal parts to give a millimeter,
while 1000 metres forms the large unit of a kilometer.

Mass is measured
in multiples of gram and time in multiples of a second.