LS, I am having some trouble using user-defined units and dimensionless once. Consider the example (taken straight from the documentation) that defines nautical miles (added at the bottom). When I do the following on VS2010: typedef quantity<boost::units::nautical::length> TDistanceInNMI; typedef quantity<dimensionless> TDimLess; TDistanceInNMI nm1,nm2,nm3; TDimLess d; nm1 = nm2 + nm3; // compiles OK nm1 = d*nm2; // compiles OK nm1 = nm2 + d*nm3; // does not compile, claims there is no operator+ defined I suppose I might have to add a dimensionless type to the 'nautical' system, or have some misconceptions on how this should work. I tried adding the following line (mimicking some of the internal stuff) but that did not due to trick: typedef unit<dimensionless_type,system> dimensionless; Could anyone tell me whether there is there anything I need to define to make this work? Any help is appreciated, Many thanks, Pieter --- The example --- namespace boost { namespace units { namespace nautical { struct length_base_unit : base_unit<length_base_unit, length_dimension, 1000> { static std::string name() { return "nautical mile"; } static std::string symbol() { return "nmi"; } }; typedef make_system<length_base_unit>::type system; typedef unit<length_dimension,system> length; // 'typedef unit<dimensionless_type,system> dimensionless'; static const length mile,miles; } } } // helper for conversions between nautical length and si length BOOST_UNITS_DEFINE_CONVERSION_FACTOR(boost::units::nautical::length_base_uni t, boost::units::si::meter_base_unit, double, 1.852e3); Pieter