Some functions do not take any argument and return constant values that represent units of measurement. They include units of the SI system of measurement used internationally and which, by international agreement, have a value of 1. The unit of time is the second, the unit of length is the meter, the unit of mass is the kilogram, and so on.

second `= 1`

meter `= 1`

kg `= 1`

Other unit functions return values defined by reference to these basic SI units. AddUp defines many of these for commonly-used measures, all expressed in SI units:

minute `= 60`

day `= 86,400`

pound `= 0.45359`

mile `= 1,609.344`

Functions *minute* and *day* return the number of
seconds (the unit of time) in a minute and a day. Function *pound*
gives the number of kilograms (the unit of mass) in a pound. Function
*mile* gives the number of meters (the unit of length) in a
mile.

Unit values can be directly used in expressions. The number of seconds in three weeks is:

3 * week `= 1,814,400`

Multiplications are implied when the multiplication operator is omited before the name of a function. This means what we can also write:

3 weeks `= 1,814,400`

Operations that involve units, even different units, can be combined:

3 weeks + 2 days `= 1,987,200`

Since unit functions return values expressed in the relevant SI unit,
the above result represents a number of seconds. AddUp 2 implements a
*->* conversion operator (as well as a *convert*
function) that lets you get a result in the units you actually need. You
can convert the above result in hours instead of seconds:

(3 weeks + 2 days) -> hours `= 552`

You can also use the conversion operator to convert units from one measurement system to another. Convert thirty degrees Celsius to Fahrenheit, convert thirty degrees of angle to radians:

30 C -> F `= 86`

30 deg -> rad `= 0.5236`

Unit functions coupled with the conversion operator provide a convenient way to handle measurement units of all sorts.