I want to define a dimension stroke_rate, or flow_rate, for that matter. Not too out of the ordinary for our application. So I am starting with something like this for my dimensions. #include <boost/units/derived_dimension.hpp> #include <boost/units/physical_dimensions/length.hpp> #include <boost/units/physical_dimensions/time.hpp> typedef boost::units::derived_dimension<boost::units::dimensionless_type,1,boost::units::time_base_dimension,-1>::type stroke_rate_dimension; typedef boost::units::derived_dimension<boost::units::length_dimension,3,boost::units::time_dimension,-1>::type flow_rate_dimension; typedef boost::units::unit<ourns::units::stroke_rate_dimension,boost::units::si::system> stroke_rate; typedef boost::units::unit<ourns::units::flow_rate_dimension,boost::units::si::system> flow_rate; However, I am receiving compiler errors when I try and include the units, Error 1 error C2039: 'value' : is not a member of 'boost::units::detail::dimension_list_tag' C:\Source\Simulations\tools\boost-msvc90-pro\boost\mpl\aux_\preprocessed\plain\less.hpp 20 CS.Calculations.Managed Error 2 error C2065: 'value' : undeclared identifier C:\Source\Simulations\tools\boost-msvc90-pro\boost\mpl\aux_\preprocessed\plain\less.hpp 21 CS.Calculations.Managed Error 3 error C2039: 'value' : is not a member of 'boost::units::detail::dimension_list_tag' C:\Source\Simulations\tools\boost-msvc90-pro\boost\mpl\aux_\preprocessed\plain\less.hpp 21 CS.Calculations.Managed Error 4 error C2065: 'value' : undeclared identifier C:\Source\Simulations\tools\boost-msvc90-pro\boost\mpl\aux_\preprocessed\plain\less.hpp 22 CS.Calculations.Managed And so on along these lines. What am I doing wrong with the units and/or dimensions? This is quite similar to energy_density_dimension, for example. typedef derived_dimension<length_base_dimension,-1,mass_base_dimension,1,time_base_dimension,-2>::type energy_density_dimension; However, I am failing to see any appreciable difference. Any thoughts? Thanks, Michael