Reflection Grating Spectrometer (RGS) spectra of the central 3.4 arcmin regions of Abell 3526 (left) and NGC 5813 (right) in the 10 − 21 Å band fitted with different models. Panel a: fits by the two-temperature cie with model 1, the residuals are shown in panel b. Panels c and d: residuals of the fits with models 2 and 0, respectively. Panel e: ratios among the three model spectra. The model 0 to model 1 ratios are plotted in blue, and the model 2 to model 1 ratios are plotted in red. It can be seen that the line emissivities of model 1 are higher than those of model 0, but slightly lower than those of model 2, in the 15 − 17 Å band.