Standard unit of measurement

In physics we can say any other value of the physical quantity can be expressed as a simple multiple of the unit of measurement.For example, length is a physical quantity. The metre is a unit of length that represents a definite predetermined length. When we say 10 metres (or 10 m), we actually mean 10 times the definite predetermined length called “metre”.
In ancient times, man used the length of a foot,the width of a finger, and the distance of a step were commonly used as different units of measurements.
In ancient times people of the Indus valley civilisation must have used very good measurements of length because we see evidence in excavations of perfectly geometrical constructions.
For Example
Each metre (m) is divided into 100
equal divisions, called centimetre (cm).
Each centimetre has ten equal divisions,
called millimetre (mm). Thus,
1 m = 100 cm
1 cm = 10 mm
For measuring large distances, metre
is not a convenient unit. We define a
larger unit of length. It is called
kilometre (km).
1 km = 1000 m