  We aim to examine the relative cross-calibration accuracy of the on-axis
effective areas of the XMM-Newton EPIC pn and MOS instruments. Spectra from a
sample of 46 bright, high-count, non-piled-up isolated on-axis point sources
are stacked together, and model residuals are examined to characterize the EPIC
MOS-to-pn inter-calibration. The MOS1-to-pn and MOS2-to-pn results are broadly
very similar. The cameras show the closest agreement below 1 keV, with MOS
excesses over pn of 0-2% (MOS1/pn) and 0-3% (MOS2/pn). Above 3 keV, the MOS/pn
ratio is consistent with energy-independent (or only mildly increasing)
excesses of 7-8% (MOS1/pn) and 5-8% (MOS2/pn). In addition, between 1-2 keV
there is a `silicon bump' - an enhancement at a level of 2-4% (MOS1/pn) and
3-5% (MOS2/pn). Tests suggest that the methods employed here are stable and
robust. The results presented here provide the most accurate cross-calibration
of the effective areas of the XMM-Newton EPIC pn and MOS instruments to date.
They suggest areas of further research where causes of the MOS-to-pn
differences might be found, and allow the potential for corrections to and
possible rectification of the EPIC cameras to be made in the future.
