In the Cookbook of the ISOCAM Observer's Manual one often speaks of observing times while in PGA the number of exposures has to be entered. Also the definition of N is not always correct in the ISOCAM Observer's Manual. For this reason we recall here the definition of the quantity N . One should remeber that it depends on the AOT.
where
is the on source position,
is the reference off source position one and
is the last reference off source
position.