How further systematic effects change the obtained Perseus (left panel) and Coma (right panel) redshifts. For each region, the ends of the leftmost (red) bars are the results for the joint and for the total spectral fits, using the APEC model. The ends of the centre (blue) bars are the results using the APEC and using the SPEX spectral models, when fitting the total spectra. The right (green) points show the effect of using a continuum for the SPEX model which is for a temperature which is 10 per cent greater or less than the line temperature, fitting the total spectra.