This update for units fixes the following issues:

units 2.21:

* Fix bug arising when some environment variables are undefined
* Improve error reporting when input files are missing or invalid

units 2.20:

* Add abs(), ceil(), round(), floor(), Gamma(), lnGamma(),
factorial(), erf() and erfc() functions.
* Add densities of all of the elements
* Add several new unit systems
* Add --conformable option which noninteractively prints a list
of all units conformable with a specified a specified unit
* Invoke the pager more intelligently depending on the size of the
screen
* Fix bug where unit lists conversions displayed excess precision
(e.g. non-integer output for integer input)
* Display precision warning when conversion to unit lists uses
all of the available precision

units 2.19:

* Unit definitions updated to reflect new 2019 revisions to SI
and the 2018 NIST CODATA.
* Added definitions of country and USA state areas, and physical
properties of selected woods.
* Changes only to definitions.units in this release.

units 2.18:

* The units_cur script now supports multiple currency sources
* Add hyperbolic functions: sinh, cosh, tanh, asinh, acosh, atanh
* Add log to arbitrary integer bases: log3, log4, log72, etc.
* Units can be redefined without a warning by adding '+' before
the unit name in definitions.units.
* Add 'quit' and 'exit' commands.
* Add support for CGS electromagnetic units (activated using the
-u option or the UNITS_SYSTEM environment variable)
* Add !prompt command to add a prefix to the "You have:" prompt
* Texts specified with !message appear in the log file

units 2.17:

* Updates to units database
* Update units_cur to handle bad records returned by yahoo server
* Move currency.units out of /usr/share because the file is not
static and /usr/share is supposed to house static files.
The new location is $sharedstatedir which may be /var/lib