In retrospect I think I am using BOOST_CHECK_CLOSE_FRACTION incorrectly. What I want to do is take two values and compute their absolute variance. I want to then take that variance and determine if it is greater than (failure) or less than or equal a tolerance (success). I think I need to use BOOST_CHECK _LE instead as follows: double a = 1.0e-12; double b = 1.0e-13; double tolerance = 1.0e-12; BOOST_CHECK_LE ( fabs ( a - b ), tolerance ); So I could make a macro called: /*! * \brief Check the absolute variance between two floating point or double values * \param L left float/double value * \param R right float/double value * \param T tolerance of comparison */ #define BOOST_CHECK_VARIANCE( L, R, T ) BOOST_CHECK_LE ( fabs ( L - R ), T ) Stephen Stephen Torri, PhD NAVAL SURFACE WARFARE CENTER DAHLGREN 17214 Ave B Suite 121 Dahlgren, Va. 22448 540-653-1082 I am not a contracting officer. I cannot modify or initiate contracts, nor do I have the authority to financially commit the government in any way.