CAM03 uses a spatial modulation: the background is measured with the same pixel, first on the source and next on a nearby empty reference field. Assuming that it has the same intensity in both observations, it can be accurately subtracted, regardless of the flat-field accuracy. The limitation of this technique is the small scale spatial structure of the background, which is not known at this time. Extrapolation towards high spatial frequency of the power spectrum of these fluctuations in the IRAS data indicates that this sensitivity limitation should be at a very low flux level.
Using only one reference is the normal case, but CAM03 allows to take 1 to 4 different reference fields. This possibility allows to average out a large scale gradient in the background.
Each passage on a field is a pointing. The same number of exposures
is taken at each pointing, whether source or
reference field, so that the total time spent on the source is the
same as the total time spent observing reference fields. The fields
are observed in the same sequence, defined by the observer, for all
the observations within an AOT CAM03: Source 
Ref1
Source Ref2 etc.
This sequence defines a cycle of pointings. In the absence of low
frequency noises (drift etc.), the observation can be completed in one
cycle. Nevertheless, if 
is large, it may be
better to split the observation in several cycles, at some slew time
overhead expense. The observer should limit the total duration of a
cycle to 20 minutes, and split the observation in several cycles if
this limit is exceeded.
A cycle of pointing is always performed in the same optical
configuration, but, within a single CAM03, always using the same
set of fields, it is possible to make observations with up to 64
different optical configurations (channels, filter or CVF
, PFOV).
Raster scans, CVF scans, polarimetric observations, and the FLASH-MODE of the SW channel are not supported in CAM03. Still, the CVF can be used as a narrow band pass filter as in CAM01.
The total time 
spent for an observation is the sum
of the 3 terms:
which are described in sections 
,
and