We desire a simple comparison of the absolute effective areas of the current generation of CCD instruments onboard the following observatories: Chandra ACIS-S3, XMM-Newton (EPIC-MOS and EPIC-pn), Suzaku XIS, and Swift XRT and a straightforward comparison of the time-dependent response of these instruments across their respective mission lifetimes. We have been using 1E 0102.2-7219, the brightest supernova remnant in the Small Magellanic Cloud, to evaluate and modify the response models of these instruments. 1E 0102.2-7219 has strong lines of O, Ne, and Mg below 1.5 keV and little or no Fe emission to complicate the spectrum. As part of the activities of the International Astronomical Consortium for High Energy Calibration (IACHEC), we have developed a standard spectral model for 1E 0102.2-7219. The model is empirical in that it includes Gaussians for the identified lines, an absorption component in the Galaxy, another absorption component in the SMC, and two thermal continuum components. In our fits, the model is highly constrained in that only the normalizations of the four brightest lines/line complexes (the O vii He$alpha$ triplet, O viii Ly$alpha$ line, the Ne ix He$alpha$ triplet, and the Ne x Ly$alpha$ line) and an overall normalization are allowed to vary. We have examined these measured line fluxes as a function of time for each instrument after applying the most recent calibrations that account for the time-dependent response of each instrument. We perform our effective area comparison with representative, early mission data when the radiation damage and contamination layers were at a minimum. We find that the measured fluxes of these lines generally agree to within +/-10% for all instruments, with 38 of our 48 fitted normalizations within +/-10% of the IACHEC model value.
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