Dear chrono maintainer team, Using the following example : int main(int argc, char **argv) { boost::chrono::process_real_cpu_clock::time_point start = boost::chrono::process_real_cpu_clock::now(); for ( long i = 0; i < 1000; ++i ) std::sqrt( 123.456L ); // burn some time Sleep(10000); //idle some time boost::chrono::process_real_cpu_clock::time_point end = boost::chrono::process_real_cpu_clock::now(); std::cout << end << std::endl; boost::chrono::process_real_cpu_clock::duration elapsed = (end - start); std::cout << "took real : " << elapsed << "nanoseconds\n"; return 0; } I obtain negative times. I run boost 1.49 win32 on Windows 7 x64 with Visual studio 2010. Studying the behavior of the timer, I think that the error is one of these : - process_real_cpu_clock::now() only stores the current time in a 32 bit integer instead of a 64 bit integer - time_points only prints the 32 lowest bits. I came to this conclusion by observing the results printed before they got negatives (printing in the loop with the sqrt): 2019000000 nanoseconds is the last value printed before getting negative. Is there any mistake in my way of using this chronometer ? Do you have a workaround ? Thank you for your help ! Wilfried K. ----- Cordialement, Wilfried Kirschenmann "An expert is a person who has made all the mistakes that can be made in a very narrow field."* *Niels Bohr - *Danish physicist (1885 - 1962)*