Dear List, I would like to calculate a shear stress based on a shear rate and a viscosity using Boost.Units. Here I have problems using derived dimensions and conversion factors based on a existing system. The error messages of my compiler are in German, so I tried to document my problems with a test code: #include #include "stress.h" #include "shearrate.h" namespace bu = boost::units; namespace SI = bu::si; main(){ //Define a quantity of unit stress. Unfortunately there is no //realization of the defined physical dimension stress in si. //So a user defined type from stress.h (see below) is used: bu::quantitySI::stress WSS_x; //Define a shear rate. I did not understand how to use a //inverse time as dimension. Therefore I defined the derived //dimension per_time in shearrate.h. Is it possible to add it to //the si system (as I tried) or do I have to define //my own system and a conversion factor? bu::quantitySI::per_time WSR_x(1*per_second); //There is a existing si type for the dynamic viscosity. //However, there is no defined constant. How is the //correct way to assign a value? Should I define this //constant? bu::quantitySI::dynamic_viscosity eta; //Calculation of the shear stress. It seems that this calculation //tries to use a »sizeof« on eta, that seems to have a // incomplete type //(»boost::STATIC_ASSERTION_FAILURE<false>«). And there //seems to be something wrong with the conversion. //Do I have to define a conversion factor? Or is this error //caused by my previous mistakes? WSS_x=WSR_x/eta; } Included header file 1: #include #include #include namespace boost { namespace units { namespace si { typedef unit stress; } // namespace si } // namespace units } // namespace boost Included header file 2: #include #include #include #include #include #include #include #include namespace boost { namespace units { namespace si { typedef derived_dimension< time_base_dimension,-1>::type per_time_dimension; // [1/m] typedef unit< si::per_time_dimension, si::system > per_time; static const per_time per_second; static const per_time per_seconds; } } } Thank you, André