It selects the used receiver band(s), establishes defaults for data presentation, reports on the amount of correlations obtained, scan ranges between tunings, array configuration(s), lists the physical baselines and antennas, builds a first flux list and reports on the tuned band. In addition, it defines internal variables which are later used by the calibration procedures.
The procedure also selects the RF calibrator, at first the brightest observed source, otherwise that selected in a previous RF calibration. The selection is reported in the line of commands, as shown in Figure . Sometimes, because of technical problems or to improve sensitivity, another calibrator must be considered. In those cases ``let band_source `a_new_calibrator' '' must be typed in CLIC to select `a_new_calibrator'.
Select deduces which are the phase calibrators observed alternatively with the source, hence suitable to calibrate phase and amplitude evolution in time. The names of the selected calibrators are stored in the variable phcal. You can decide about the content of phcal as follows: ``let phcal `calibrator1' ` calibrator2' ... ''. Note that ``let phcal `*' '' should be selected if the (frequency averaged) phases from the H and V polarization receivers are not identical, which for instance can be seen in the RF phases plot in the First Look (see more details in Sect. ).
By default, the atmospheric phase corrections derived from the 22GHz receivers are used according to the PhCor evaluation (see Sect. ). However, sometimes it is recommended (by the Autoflag procedure or by the AoD) not to use the phase corrections, for instance due to problems with the 22GHz receivers. ``let do_atm no'' allows ignoring the atmospheric phase corrections.
Several gain ranges: From time to time, the Select procedure pauses to inform on the presence of different gain ranges, i.e. scan intervals with different tuning characteristics. The RF calibration is then performed independently for each gain range ( i), and a calibrator is so assigned to the variable ``band_source[i]'' for each range. When the procedure pauses, continue should be typed in the line of commands to continue.