1.2.3 Conventions for the use of SI Units

(1) Unit of every physical quantity should be represented by its symbol.

(2) Full name of a unit always starts with smaller letter even if the name is after a person,

e.g., 1 newton, 1 joule, etc.

But symbol for unit named after a person should be in capital letter,

e.g., N after scientist Newton, J after scientist Joule, etc.

(3) Symbols for units do not take plural form

for example, force of 20 N and not 20 newtons or not 20 Ns.

(4) Symbols for units do not contain any full stops at the end of recommended letter,

e.g., 25 kg and not 25 kg..

(5) The units of physical quantities in numerator and denominator should be written as one ratio

for example the SI unit of acceleration is m/s^2 or m s^-2 but not m/s/s.

(6) Use of combination of units and symbols for units is avoided when physical quantity is expressed by combination of two.

e.g., The unit J/kg K is correct while joule/kg K is not correct.

(7) A prefix symbol is used before the symbol of the unit. Thus prefix symbol and units symbol constitute a new symbol for the unit which can be raised to a positive or negative power of 10.

1ms = 1 millisecond = 10^-3s

1s = 1 microsecond = 10^-6s

1ns = 1 nanosecond = 10^-9s

Use of double prefixes is avoided when single prefix is available 10^-6s =1s and not 1mms. 10^-9s = 1ns and not 1ms

(8) Space or hyphen must be introduced while indicating multiplication of two units

e.g., m/s should be written as m s^-1 or m-s^-1 and Not as ms^-1 (because ms will be read as millisecond).