How the data look like

Let us assume that we are already looking at the data, in CLIC. After typing in CLIC find and later list we will see, e.g.:

60 7684 QA12 3C454.3      P CORR CO10     6Cq-N17      12-NOV-2007 21:58  2.9
61 7685 QA12 3C454.3      P CORR CO10     6Cq-N17      12-NOV-2007 21:59  2.9
62 7686 QA12 3C454.3      P CORR CO10     6Cq-N17      12-NOV-2007 22:00  2.9

where each line corresponds to an observation subscan⁵. Each subscan contains the following information:

 - First column: Observation number
 - Second column: Scan number
 - Third column: Project name       
 - Fourth column: Source name
 - Fifth column: Type of source (O=object, P=phase calibrator)
 - Sixth column: Type of scan procedure
 - Seventh column: Line name
 - Eighth column: Array configuration, i.e. antenna positions
 - Nineth column: Date
 - Tenth column: UT time
 - Eleventh column: Hour angle

The usual observational procedures (column sixth) and characteristics are:

 CORR: cross-correlation; 1 subscan (ss) is obtained per scan 
 GAIN: cross-correlation to measure the sideband rejection; 1 ss
 FOCU: focus measurements in all the antennas; 5 ss
 POIN: interferometric pointing in all the antennas; 2 ss
 FLUX: cross-correlation to measure the flux; 1 ss
 IFPB: IF passband calibration, by observing a noise diode; 2 ss
 AUTO: autocorrelation; 1 ss
 CALI: atmospheric calibration, autocorr. on SKY, HOT [COLD] load; 2 [3] ss
 SKYD: sequence of autocorrelations to calibrate the 22 GHz receivers; 12 ss

By using the mentioned procedures, a typical sequence of observations is:

 - Receiver tuning followed by a sideband gain measurement
 - Radio frequency passband calibration on a bright source
 - Acquisitions on at least a flux calibrator, MWC 349 if possible
 - Check the pointing and focus on the predefined phase calibrator(s)
 - Possibly a flux measurement on this calibrator(s)
 - Cross-correlations on the phase calibrator(s)
 - Cross-correlations on source

About 3 minutes are spent on each phase calibrator, some more time if pointing and focus are performed, every $\sim$ 23 minutes on source. Pointing and focus are normally repeated every two transitions of $\sim$ 23 minutes on source. IFPB, AUTO and CALI scans are obtained before correlations to calibrate the observations in real time (see Sect. ).