It is possible to produce a spectrum from combined instruments using the tasks rgscombine or epicspeccombine. The combined spectra have an undetermined contribution from each instrument and so assumptions have to be made when grouping the spectra. For simplicity, specgroup uses the settings of MOS1 if the spectrum has been made from a combination of EPIC cameras and the settings of RGS2 if made from a combination of RGS1 and RGS2.