Hi John, I have added the new undeterminate_result_error to the framework, used it in the pow function, and checked into the sandbox. Please could you tell me if all looks good to you? In test_error_handling.cpp, I noticed that not every policies were tested: ignore_error and errno_on_error were missing. I added some test for them with undeterminate_result_error, do you want me to do the same for the other types of error? It's pretty straight-forward now. I haven't been able to add a test to the last part of test_policy_2.cpp, where you test different overloads of make_policy(). I wanted to add the same test as at line 103, it didn't pass. I reduced the line until I end up with this: BOOST_CHECK(check_same( make_policy(undeterminate_result_error<ignore_error>()), policy<undeterminate_result_error<ignore_error> >() )); But it still doesn't pass. I guess it's a problem with the way in which I integrated the new error in the normalise class but I'm a bit confused about what to do exactly... Also, test_tr1 doesn't pass for me but I guess it's not related to my modifications...? Regards Bruno