Variation in E_cut and kT_e with the observation epochs as obtained from the xillver and xillverCP model fits, respectively, to the spectra of NGC 3227. The plotted errors were calculated using the χ² = 2.71 criterion, i.e. 90% confidence range. The dashed black lines in each panel are fits of constant (mean of E_cut and kT_e) to the data points. For the fitting, epochs in which we were unable to constrain E_cut and kT_e were dropped (indicated with red diamonds).