For the shorter wavelengths (2.36-16 microns) 
Lyrae is being used as
the primary in-orbit calibration source. For the longer wavelengths, the
asteroids Ceres and Pallas initially were chosen as the primary calibration
sources. Unfortunately, the solar system tracking performance of the ISO
satellite was disturbing the measurements. Therefore, NML-CYG has been
observed with the calibration uplink procedure in order to uncover possible
big discrepancies between lab and in-orbit measurements.