UNIT: there is a need of some standard quantites for measuring unknown quantities.Once a stanfard is set for a quantity then Powered by www.testvitals.com 2018/11/11 07:58 it can be expressed in tems of that standard quantity .This standard quantity is called a unit. System of Units:The eleventh General conference on weight and measues held in pairs is 1960 adopted a world wide system of measurements calle system of units.