Metrics
SI-International System of Units

SI-International System of Units ... image and brief descriptions

Burgess COMMENTARY

Peter Burgess

The seven SI base units and the interdependency of their definitions. Clockwise from top:

• kelvin (temperature),

• second (time),

• metre (length),

• kilogram (mass),

• candela (luminous intensity),

• mole (amount of substance) and

• ampere (electric current).

The second of time, kelvin and kilogram are defined independently of any other base units.

The metre is defined in terms of the speed of light, so depends upon the definition of the second.

The definitions of the other base units are more complicated.