In setting up a test for math function accuracy, I incorrectly coded thus: BOOST_CHECK_EQUAL(sin(0.5), 0.479426); and got the somewhat puzzling - apparently wrong - message error in "call_test_main": test sin(0.5) == 0.479426 failed [0.479426 != 0.479426] On most days of the week, one would expect [0.479426 == 0.479426]! I should of course have written BOOST_CHECK_EQUAL(sin(0.5), 0.47942553860420301); (or used BOOST_CHECK_CLOSE(sin(0.5), 0.47942553860420301, 1e-16);) But I wonder if the test program would be even more helpful if it output all possibly significant digits. In test_tools.hpp, I have added an increase to the ostream precision (default only 6 digits) int print_log_value thus template<typename T> struct print_log_value { void operator()( std::ostream& ostr, T const& t ) { if(std::numeric_limits<T>::is_specialized && std::numeric_limits<T>::radix == 2) { // Show all possibly significant digits (for example, 17 for 64-bit double). ostr.precision(2 + std::numeric_limits<T>::digits * 301/1000); } ostr << t; // by default print the value. } }; so that the message is no longer test sin(0.5) == 0.479426 failed [0.47942553860420301 != 0.47942600000000002] and my folly obvious. And after the original mistake is corrected BOOST_CHECK_EQUAL(sin(0.5), 0.47942553860420301); The log file reports: info: sin(0.5) == 0.47942553860420301 passed. Paul PS (It does not appear to possible to change the precision 'externally' by calling cout.precision(17); myTestLog.precision(17); probably because ostr in test is contructed with default precision). Paul A Bristow Prizet Farmhouse, Kendal, Cumbria UK LA8 8AB +44 1539 561830 +44 7714 330204 mailto: pbristow@hetp.u-net.com