Estimating the rotation period uncertainty for the case h_peak >  0.3. The measured rotation period P_rot is given on the x-axis. On the y-axis, the mean and standard deviation of the absolute difference of the periods P1 and P2 is given within period bins of one day. The green curve shows a fit to the data (using equal weights), and the red curve shows a similar fit estimated from Kepler data (see Fig. B.2).