  We present a flux calibration scheme for the PACS chopped point-source
photometry observing mode based on the photometry of five stellar standard
sources. This mode was used for science observations only early in the mission.
Later, it was only used for pointing and flux calibration measurements. Its
calibration turns this type of observation into fully validated data products
in the Herschel Science Archive. Systematic differences in calibration with
regard to the principal photometer observation mode, the scan map, are derived
and amount to 5-6%. An empirical method to calibrate out an apparent response
drift during the first 300 Operational Days is presented. The relative
photometric calibration accuracy (repeatability) is as good as 1% in the blue
and green band and up to 5% in the red band. Like for the scan map mode,
inconsistencies among the stellar calibration models become visible and amount
to 2% for the five standard stars used. The absolute calibration accuracy is
therefore mainly limited by the model uncertainty, which is 5% for all three
bands.
