For estimating the observing times it is strongly recommended to use
the ISOCAM software simulator (see Section 5.1.1 in the ISOCAM
Observer's Manual). The software estimator gives a very good
approximation of the signal-to-noise ratio of a particular
observation. Of course the simulator cannot account for all systematic
effects, one example being that the time estimator does not include a
simulation of cosmic ray impacts. Note also that the simulator gives
only an estimate of the observing time 
while in PGA one
has to enter the number of exposures N
and stabilisation frames
N
. Furthermore, the simulator does not account for various time
buffers such as security times between each telecommand blocks and
other overheads, which finally will end up in the target dedicated
time (TDT) for a single AOT. As an example of up-link time,
transmitting an observation can last from a few tens of seconds to
more than 100s, depending on its complexity. One also has to
consider that buffer times are subject to changes.
Thus, a mathematical correct calculation of the TDT can only be done by having a copy of each telecommand and adding all individual times together. This is the excercise done during Phase II entry by running the logic or using PGA.
Here, for the Phase I, one needs a good approximation of the observing
time of the proposal. For a quite realistic estimate of the actual
time required to perform an observation one should increase the
on the X-axis of ISOCAM's simulator by 
.