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Fig. 4


Proportion of the solar disc covered by faculae, nfac in the MDI (red) and HMI (black) data sets over the period of overlap. The solid red line gives the final result which incorporates the cross-calibration of the magnetogram signal and nfac in the MDI data set (see text). The dotted red line shows the level if we omit the adjustment to nfac and the dashed red line that from the original MDI data.

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