B.2 Representation
UCUM can represent any number of valid units derived from 7 basic units. To that end, the standard combines various components:
Basic units
metre (m, length)
second (s, time)
gram (g, mass)
radian (rad, angle)
Kelvin (K, temperature)
Coulomb (C, electric charge)
candela (cd, luminous intensity)
derived units with conversion factors and formulas for the reduction to base units
prefixes, i.e. a list of 30 standard prefixes to generate multiples (e.g. k for kilo, multiplier 10³) or fractions (e.g. d for deci, multiplier 10-1) of measurement units
symbols and operators as well as syntax rules for their combination as follows:
| <sign> | ::= | “+” | “-” |
| <digit> | ::= | “0” | “1” | “2” | “3” | “4” | “5” | “6” | “7” | “8” | “9” |
| <digits> | ::= | <digit><digits> | <digit> |
| <factor> | ::= | <digits> |
| <exponent> | ::= | <sign><digits> | <digits> |
| <simple-unit> | ::= | <ATOM-SYMBOL> | <PREFIX-SYMBOL><ATOM-SYMBOL[metric]> |
| <annotatable> | ::= | <simple-unit><exponent> | <simple-unit> |
| <component> | ::= | <annotatable><annotation> | <annotatable> | <annotation> | <factor> | “(”<term>“)” |
| <term> | ::= | <term>“.”<component> | <term>“/”<component> | <component> |
| <main-term> | ::= | “/”<term> | <term> |
| <annotation> | ::= | “{”<ANNOTATION-STRING>“}” |