Hi, I think I am beginning to get the boost:units library, but I still have one problem. Consider: #include <iostream> #include <boost/units/io.hpp> #include <boost/units/systems/si/length.hpp> #include <boost/units/make_system.hpp> #include <boost/units/quantity.hpp> #include <boost/units/base_dimension.hpp> #include <boost/units/base_unit.hpp> #include <boost/units/derived_dimension.hpp> // Introduce slot (measured in e.g. ffe or tfe) as a basic dimension, unit and in a system struct slot_base_dimension : boost::units::base_dimension<slot_base_dimension, 1> { }; typedef slot_base_dimension::dimension_type slot_dimension; struct ffe_base_unit : public boost::units::base_unit<ffe_base_unit, slot_dimension, 1> { static std::string name() { return("40ft equivalent"); } static std::string symbol() { return("ffe"); } }; typedef ffe_base_unit::unit_type slot_t; BOOST_UNITS_STATIC_CONSTANT(ffe, slot_t); /// derived dimension (slot) flow typedef boost::units::derived_dimension<slot_base_dimension,1,boost::units::time_base_dimension,-1>::type flow_dimension; /// placeholder class defining si unit system typedef boost::units::make_system<boost::units::si::meter_base_unit, boost::units::si::second_base_unit, ffe_base_unit>::type unit_system; typedef boost::units::unit<flow_dimension,unit_system> flow_t; BOOST_UNITS_STATIC_CONSTANT(ffe_per_second, flow_t); int main() { boost::units::quantity<flow_t> flow(4*ffe_per_second); std::cout << "flow= " << flow << std::endl; } This program outputs flow= 4 s^-1 ffe which is correct, but a bit unusual... 4 ffe/s or even 4 ffe s^-1 would have been better. Is this possible? Thanks! -- kind regards, Esben