My Visual Studio 6 requires the trigonometry functions sin, cos, etc. to be prefixed with :: in the quaternion.hpp, otherwise I get: " ...\boost-1_32\boost\math\quaternion.hpp(1686) : error C2784: 'class boost::math::quaternion<T> __cdecl boost::math::sin(const class boost::math::quaternion<T> &)' : could not deduce template argument for 'const class boost::math::quaternion<T> &' from 'const double' ...\main.cpp(112) : see reference to function template instantiation 'class boost::math::quaternion<double> __cdecl boost::math::spherical(const double &,const double &,const double &,const double &)' being compiled " I'm using a quaternion<double> here. Changing the line T d = sin(phi2); into T d = ::sin(phi2); fixes the problem (for that line). The rest of the file contains lots more trigonometry (and other math) functions, which probably also need to be prefixed. ----------------------------------------------------------------------- Job P. Mulder Xsens Technologies B.V. http://www.xsens.com