Units: A Unit Conversion Program and Scientific Calculator: Defining Unit List Aliases

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### 10.5 Defining Unit List Aliases

Unit list aliases are treated differently from unit definitions, because they are a data entry shorthand rather than a true definition for a new unit. A unit list alias definition begins with ‘`!unitlist`’ and includes the alias and the definition; for example, the aliases included in the standard units data file are

    !unitlist   hms     hr;min;sec
    !unitlist   time    year;day;hr;min;sec
    !unitlist   dms     deg;arcmin;arcsec
    !unitlist   ftin    ft;in;1|8 in
    !unitlist   usvol   cup;3|4 cup;2|3 cup;1|2 cup;1|3 cup;1|4 cup;\
                        tbsp;tsp;1|2 tsp;1|4 tsp;1|8 tsp

Unit list aliases are only for unit lists, so the definition must include a ‘`;`’. Unit list aliases can never be combined with units or other unit list aliases, so the definition of ‘`time`’ shown above could not have been shortened to ‘`year;day;hms`’.

As usual, be sure to run `units --check` to ensure that the units listed in unit list aliases are conformable.