1. When we write a unit in full, the first letter should not be in capital.
Example: metre and not as Metre kilogram and not as Kilogram
2. Name of scientist as the symbols of unit should be in upper case (capital) letter
Example: N for newton, J for joule.
3. The singular form of the unit should be used.
Example: km and not as kms, Kg and not as kgs
4. At the end of the abbreviations there should be no full stop.
Example: mm and not as mm, kg and not as kg.
5. The degree sign is omittedwhen temperature is expressed in Kelvin.
Example: 273K not as 2730 K
6. Accepted symbols should only be used.
Example: ampere is represented as ‘A’ and not ‘amp’
second is represented as ‘s’ and not ‘sec’
7. Not more than one solidus or slash should be employed. But effort should be made to avoid use of solidus or slash.
Example: J/k.mol or Jk.mol-1 but not J/k/mol
J kg-1K-1 but not J/kg/K
8. Between the number and the symbol of the unit, one letter space is always to be left.
Example: 2.3 m and not as 2.3m
Kg m s-1 and not kg ms-1
9. A physical quantity in numerical value should be expressed as p= a × 10m
Here ‘a’ is a number between 1 and 10 and ‘m’ is the appropriate power of 10.
Example: velocity of light c = 2.997 × 10 ms-1 .