The photometric calibration of ISOPHOT observations is described in this chapter. The calibration strategy for PHT-P and PHT-C using the FCS and the strategy for PHT-S, all measuring point sources, are given in Section 5.2. In the subsequent sections the extended source photometry, aperture calibration, and the PHT-S wavelength calibration are described. Section 5.6 summarizes the specific calibration procedures per AOT.
A general description of the kind of calibration files used in OLP is given in Section 5.7. Note that the uncertainties in the calibration are addressed in Chapter 9 and in the related documents `ISOPHOT Error Budgets' by Laureijs & Klaas 1999, [31] and `ISOPHOT Calibration Accuracies' by Klaas et al. 2002, [26].