The transition between the two data sets was not smooth due to the failure of two of the three available Kerr cells used to modulate circular polarization. Thus, to preserve the life of the remaining Kerr cell, the SM was pressed into service before the originally planned cross-calibration program could be undertaken. Fe I, 868.8 nm line. A cross-calibration program of closely spaced observations with both instruments was then carried out. The different constants result from the way the calibration procedures account for polarization cross-talk together with some software limitations.
Error bars are twice the standard error of the mean averaged over about a month of comparative data.
The overall scale of the DM is the better basis for absolute flux estimates, although the SM data are substantially less noisy and do not saturate in sunspots. Disk-integrated flux indices from the magnetograms show continuous and consistent variation when adjusted with the above calibration constants. The file includes corrections that put all the measurements onto the DM scale.