The basic components in the array calibration are the baseline
calibration, the pointing, and focus determinations. They must be
back fed as soon as possible to be taken into account by the real
time system. The operator must have the flexibility to suspend a
sequence of activities such as those described in a data reduction
procedure and to resume from that state (plus the manual
modifications) when the activity was suspended. He or she may
change e.g. to an other pointing source or phase calibrator. These
actions may have effects on the ongoing observing procedure. It must
be possible to modify the level of interaction at any time from
fully automated continuous processing to prompts requesting inputs
with sensible visible defaults up to prompts with no default
(i.e. fully manual).