Editing GNU Units (section)

=== GNU implementation ===
GNU ''units'' includes several extensions to the original version,<ref>{{cite web|title=Units: A Unit Conversion Program and Scientific Calculator|publisher=Free Software Foundation, Inc.|location=Boston, MA|url=https://www.gnu.org/software/units/manual/units.html|year=2014|author=Mariano, Adrian|access-date=2014-03-29}}
</ref>  including
* Exponents can be written with <code>^</code> or <code>**</code>.
* Exponents can be larger than 9 if written with <code>^</code> or <code>**</code>.
* Rational and decimal exponents are supported.
* Sums of units (e.g., <code>{{nowrap|btu + ft lbf}}</code>) can be converted.
* Conversions can be made ''to'' sums of units, termed ''unit lists'' (e.g., from degrees to degrees, minutes, and seconds).
* Units that measure reciprocal dimensions can be converted (e.g., <code>S</code> to <code>megohm</code>).
* Parentheses for grouping are supported. This sometimes allows more natural expressions, such as in the example given in [[#Complex units expressions|Complex units expressions]].
* Roots of units (e.g., <code>{{nowrap|sqrt((lbf/inch) / lb)}}</code> can be computed.
* Affine units conversions (e.g., °F to °C) are supported.
* Functions such as sin, cos, ln, log, and log2 are included.
* A script for updating the currency conversions is included; the script requires [[Python (programming language)|Python]].

Units definitions, including nonlinear conversions and unit lists, are user extensible.

The [[plain text]] database ''definitions.units'' is a good reference in itself, as it is extensively commented and cites numerous sources.