[Boost-users] [units] non-rational scaling

Dear all, I have an issue with scaled units. I tried to implement a non-rational scaling of units adapted from scale<> class (all in boost::units namespace): template<class Derived> struct non_rational_scale { static const unsigned long base = 10; typedef boost::units::static_rational<0> exponent; typedef double value_type; static double value() { return Derived::value(); } static std::string name() { return Derived::name(); } static std::string symbol() { return Derived::symbol(); } }; struct electron_volt_scale : non_rational_scale { static double value() { return 1.60218e-19; } /* elementary charge in Coulombs */ static std::string name() { return "electron volt"; } static std::string symbol() { return "eV"; } }; typedef make_scaled_unit::type electron_volt; This works fine in one direction: quantitysi::energy(1.*electron_volt()); /* gives 1.60218e-19 J. */ However, in the other direction quantity(1.*si::joule); /* gives 1 eV */ I guess, that I need some specialization for non_rational_scale to workout the correct scaling factor in the reverse direction. Thank you for your help, Matthias