I got : Calibrating the clock, for a slow timer this may take a while! Point estimate of clock overhead (t_c): 83.998 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: (-2.22045e-14 [-1.11022e-14] 0)% Timing at a nominal precision of 10%: We cannot distinguish between A and B: (-99.9794 [-98.2763] 44.4477)% Timing at a nominal precision of 2%: We cannot distinguish between A and B: (-7.69315 [-4.28203] 1.45846e+06)% Timing at a nominal precision of 0.4%: We cannot distinguish between A and B: (-2.22045e-14 [1.9685] 4.51977)% Timing at a nominal precision of 0.08%: We cannot distinguish between A and B: (-5.22489 [0.0530135] 4.15175)% So what does this means ?