I am having trouble seeing how to use mixed units. The program below compiles and runs. See the changes I "wish" I could make as comments. terry #include <boost/units/systems/si.hpp> #include <boost/units/base_units/us/foot.hpp> #include <boost/units/quantity.hpp> #include <boost/units/io.hpp> #include <iostream> #include <iomanip> using namespace std; using namespace boost; using namespace boost::units; int main() { static const si::length m = si::meter; // static const si::length ft = ???; typedef quantity<si::length> Length; Length x = 2.0 * m; Length y = 3.0 * m; // instead of "m" use "ft"; cout << "x=" << x << " y=" << y << endl; Length z = x + y; cout << "x+y=" << z << endl; // display result in "ft" return 0; } // main