Another run with larger matrix gives : Calibrating the clock, for a slow timer this may take a while! Point estimate of clock overhead (t_c): 155.994 Potential jitter on t_c (sigma_c) : 0.0168831 Increasing precision until I can discriminate between function a and b. The nominal confidence interval (minimum, [median], maximum) represents the region: 1-alpha=0.95 Timing at a nominal precision of 50%: We cannot distinguish between A and B: (-99.9507 [0] 2.22045e-14)% Timing at a nominal precision of 10%: We cannot distinguish between A and B: (-2.22045e-14 [0] 2.22045e-14)% Timing at a nominal precision of 2%: We cannot distinguish between A and B: (-1.11022e-14 [0] 0)% Timing at a nominal precision of 0.4%: A is slower than B by: (-3.16387 [-2.0155] -0.577469)%