A.4 Unit Calculations

The unit library works on strings to use them as units for numeric values. A unit string consists of

1. A positive or negative real number.
2. A sequence of unit items with exponents.
3. A fraction sign ``/'' and another sequence of unit items with exponents.

At least one of the three parts must be present. To multiply unit parts, a space or a ``*'' can be used and the exponent can be omitted if the value is one. All basic units and standard prefixes are known. This library allows to compare, multiply, divide and to calculate the square root of a unit string. The result is then converted back to a string. Two different formats are created as output, in the ``SI'' format by m * s * kg * A * K * cd or in the ``V*A'' format by m * s * V * A * K * cd commonly used for electrical problems.