AS SPACE-BASED INFRARED ASTRONOMY TRANSITIONS FROM SPITZER TO JWST THE FUNDAMENTAL ISSUE OF CROSS-CALIBRATION LOOMS LARGE ONCE AGAIN. THE ABSOLUTE PHOTOMETRIC CALIBRATION OF SPITZER'S INFRARED SPECTROGRAPH (IRS) IS TIED TO THE MULTIBAND IMAGING PHOTOMETER FOR SPITZER (MIPS) AT 24 MICRON. HOWEVER NO SIMILAR COMPARISON WAS EVER MADE WITH THE INFRARED ARRAY CAMERA (IRAC) AND IRAC WILL BE THE LINK BETWEEN SPITZER AND JWST. IN FACT THE SHORT WAVELENGTH ENDS OF THE IRS SPECTRA HAVE NEVER BEEN PINNED DOWN TO ANY MEASURED PHOTOMETRY. ADDITIONALLY A SYSTEMATIC ISSUE DUE TO MIS-CENTERINGS WITHIN THE IRS SLIT CAUSES FLUX LOSSES IN THE SPECTRA ESPECIALLY AT THE BLUE END AND THIS WAS NEVER FULLY RESOLVED DURING THE CRYOGENIC PHASE OF THE MISSION. THE FINAL SPITZER IRS DATA ARCHIVE CONTAINS OVER 20 000 SPECTRA OF OVER 14 000 OBJECTS THE LARGEST SET OF MID-INFRARED SPECTRA CURRENTLY AVAILABLE. IN ORDER TO GUARANTEE THE HIGHEST QUALITY SCIENCE RETURN OF THE IRS DATA ENHANCE THE SCIENTIFIC LEGACY OF SPITZER AND ENABLE COMPATIBILITY WITH FUTURE NASA MISSIONS THE CALIBRATION ACCURACY OF THE IRS MUST BE ENSURED. WE WILL USE OUR NEW WARM SPITZER IRAC OBSERVATIONS OF OVER 50 IRS CALIBRATION STARS COMBINED WITH THE IRS SPECTRA MIPS AND WISE PHOTOMETRY STELLAR MODELS AND TEMPLATES TO MAKE THAT POSSIBLE.