For a fraction, \fp_eval:n { 1/9000000000000000 } -> 0.0000000000000001111111111111111 displays the 16 significant digits after a long run of zeros. In that spirit I find it disconcerting that for sin(pi) \fp_eval:n { sin(pi) } -> 0.0000000000000002384626433832795 as if the 16 nonzero digits after the run of zeros are the significant ones. They are actually the 16 significant figures of \fp_eval:n {sin(pi - 0.0000000000000001)}, and "noise" as far as sin(pi) is concerned. For cos(pi/2) \fp_eval:n { cos(pi/2) } -> 0.0000000000000006192313216916398 The 16 apparently significant figures are those from \fp_eval:n { cos(pi/2 - .0000000000000001) } Rounding the cosine to 16 figures gives a 6 in the last place, which seems large to me. Perhaps sin and cos and their fellows should be given the exact value 0 at the appropriate multiples of pi/2? Andrew Parsloe