Illustration of the MgII index correction with: a) rescaled indices from LASP and Bremen, b) the BIC for model orders up to 50, c) the condition number for the same orders, d) comparison of the correction (from a 12th order model) and the ratio of the two indices and e) comparison of the index from Bremen with the corrected index from LASP, using the correction of d). All time series are lowpass filtered at 81 days.