This mode was mainly designed for the measurement of the absolute total sky brightness (e.g. Zodiacal Light, Galactic emission). For point sources a single measurement did not provide any information on the sky background for subtraction of the background contribution. In this case an extra measurement on the background had to be performed.
Absolute photometry was only possible in single filter mode. No chopped mode and no raster mode was possible.
Absolute fluxes were most accurately determined with a special procedure
including additional control and calibration measurements not offered
by the normal photometric mode. As an option the absolute
photometry sequence could be started with a measurement in dark
configuration in order to determine the actual dark current level
and improve over the average dark current behaviour established from
a set of special dark calibration measurements. Furthermore, a
measurement against the cold FCS could be selected in order to
determine external straylight contamination of the FCS measurement
and subtract that to obtain the true zero level of the FCS calibration.
The heated FCS measurement, performed after the sky measurement,
was as long as the sky measurement and usually longer than 
(in contrast to the normal mode for which a sensitivity criterion
fixed the FCS exposure in most cases to 32 sec)
which allowed a better stabilisation of the FCS measurement.
Note: Pre-flight the absolute mode was designed as chopping sky-FCS. The mode was completely revised during the mission, as this did not work properly.