Examples on the optimized selection of the Fourier order. Left column: normalized standard deviation of the Fourier fit as a function of the Fourier order. Red line shows the robust linear regression to the data in N_FOUR = 100 − 150. Right column: fit variances over the standard deviation of the fit variance at N_FOUR = 150. Vertical yellow stripes show the optimum Fourier orders derived from the statistics given in the header. See text for further details.