(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,
(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/s2
or m s-2 but
(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 1µs = 1 microsecond = 10-6s 1ns = 1 nanosecond = 10-9s Use of double prefixes is avoided when single prefix is available 10-6s =1µs and not 1mms. 10-9s = 1ns and not 1mµs
(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).