I realize that the Units libary is still a work-in-progress, but I thought you might like to know about these failures. Using 1.35.0 with the latest Units code (SVN rev. 45355) and using GCC 4.1.2, I get these failures in test/: test_limits, test_cmath The exact compilation errors are in the file attached. Also, I cannot compile this simple test code. I may very well be doing something wrong: #include <boost/units/systems/si.hpp> #include <boost/units/systems/other/foot.hpp> #include <boost/units/systems/detail/non_si_unit.hpp> BOOST_UNITS_NON_SI_UNIT(survey, yard_per_sec, yard_per_sec, 0.3048006 * 3.0, boost::units::SI::velocity, 53); typedef boost::units::quantity<boost::units::survey::yard_per_sec_base_unit, double> YardsPerSec; int main() { YardsPerSec yps1; YardsPerSec yps2; yps1 -= yps2; } The errors are: g++ test_non_si_units.cpp -o test -g -I /usr/local/include/boost-1_35 /usr/local/include/boost-1_35/boost/units/quantity.hpp: In member function 'boost::units::quantity<Unit, Y>& boost::units::quantity<Unit, Y>::operator-=(const boost::units::quantity<Unit2, YY>&) [with Unit2 = boost::units::survey::yard_per_sec_base_unit, YY = double, Unit = boost::units::survey::yard_per_sec_base_unit, Y = double]': test_non_si_units.cpp:14: instantiated from here /usr/local/include/boost-1_35/boost/units/quantity.hpp:233: error: invalid application of 'sizeof' to incomplete type 'boost::STATIC_ASSERTION_FAILURE<false>' There appear to be no tests defined for the non-SI parts of Units, which is probably why this has gone unnoticed (if indeed it has). HTH, Zach