S

Alphabetical index

second (plane angle)

Unit of measurement of plane angle, non-SI but accepted for use with SI, symbol: ″.

second (time)

Unit of measurement of time, symbol: s.

septillion

1000 sextillion, or 10²⁴. The value of the prefix “yotta”.

sextillion

1000 quintillion, or 10²¹. The value of the prefix “zetta”.

SI

The International System of Weights and Measures, agreed in 1960, and since 1995 the UK’s primary system of measurement for most purposes.

siemens

Unit of measurement of electrical conductance, symbol: S.

sievert

Unit of measurement of dose equivalent of radiation, symbol: Sv.

steradian

Unit of measurement of solid angle, symbol: sr.

symbols

Symbols for units are written in a roman font (regular upright) and should not be amended, italicised or pluralised. They are also written lower case, except the symbol L and symbols named after persons e.g. the symbol W for watt named after the Scottish engineer, James Watt.

Symbols for prefixes should be in lower case, except for those meaning a multiple greater than one thousand.

e.g. 3 kilowatts is 3 kW, not 3 Kw or 3 KW or 3 kw, and 500 megawatts is 500 MW.