hmmm...decided to try and test this guy out and based on the docs I would think the following code would compile, but it doesn't in VC++ 8.0...g++ gobbles it up ok though. #include <boost/units/quantity.hpp> #include <boost/units/io.hpp> #include <boost/units/systems/si_units.hpp> using namespace boost::units; using namespace boost::units::SI; int const TEST_LIMIT = 5000000; quantity<volume> f_mcs(quantity<length> x, quantity<length> y, quantity<length> z) { static quantity<length> const C = 3.14 * meters; quantity<volume> r = 0 * cubic_meters; for (int i = 0; i < TEST_LIMIT; ++i) r = r + ((x + y) * z * C); return r; } int main() { } output: 1>profile_units.cpp 1>.\profile_units.cpp(22) : error C2752: 'boost::units::add_typeof_helper<X,Y>' : more than one partial specialization matches the template argument list 1> with 1> [ 1> X=boost::units::quantity<boost::units::SI::length>, 1> Y=boost::units::quantity<boost::units::SI::length> 1> ] 1> C:\Documents and Settings\nroberts\Desktop\mcs_units_v0.5.5\units\boost/units/quantity.hpp(296): could be 'boost::units::add_typeof_helper<boost::units::quantity<Unit,Y>,boost::units::quantity<Unit2,Y>>' 1> C:\Documents and Settings\nroberts\Desktop\mcs_units_v0.5.5\units\boost/units/operators.hpp(71): or 'boost::units::add_typeof_helper<X,X>' 1>.\profile_units.cpp(22) : error C2893: Failed to specialize function template 'add_typeof_helper<boost::units::quantity<Unit,Y>,boost::units::quantity<Unit2,Y>>::type boost::units::operator +(const boost::units::quantity<Unit,Y> &,const boost::units::quantity<Unit2,Y> &)' 1> With the following template arguments: 1> 'boost::units::SI::length' 1> 'boost::units::SI::length' 1> 'double' 1> 'double' 1>.\profile_units.cpp(22) : error C2784: 'add_typeof_helper<boost::units::unit<System,Dim>,boost::units::unit<System,Dim2>>::type boost::units::operator +(boost::units::unit<System,Dim>,boost::units::unit<System,Dim2>)' : could not deduce template argument for 'boost::units::unit<System,Dim>' from 'boost::units::quantity<Unit>' 1> with 1> [ 1> Unit=boost::units::SI::length 1> ] 1> C:\Documents and Settings\nroberts\Desktop\mcs_units_v0.5.5\units\boost/units/unit.hpp(154) : see declaration of 'boost::units::operator +' 1>.\profile_units.cpp(22) : error C2676: binary '+' : 'boost::units::quantity<Unit>' does not define this operator or a conversion to a type acceptable to the predefined operator 1> with 1> [ 1> Unit=boost::units::SI::length 1> ]