physical is a C++ library that enables computation with physicalquantities, units and constants. Both compiletime and runtime compatibility checks are available as well as stream input and output.
physical is hosted on http://sourceforge.net/projects/physical/. Currently only source and header files are provided; no binary distribution is available. You may obtain the files using the svn access (you might therefore need to install a subversion client like TortoiseSVN or the like).
This library is still under development and incompplete, thus pre-alpha. There may be differences between the documentation and the actual code. The documentation may in some cases lag behind the impelementation or be way ahead of it in other cases.