A complete observation is made up of a number of scans.
Observations typically alternate between program source scans and calibrator scans.
Details of scans are kept in a schedule file . The schedule file also defines the frequencies, integration averaging unit and correlator setup to use. If your observation involves looking at five or more sources you are advised to create a text format schedule file as described below. It is often the case with synthesis instruments that system errors lead to artefacts at the centre of the field. It is therefore advisable to displace the source position a few synthesised beamwidths from the field centre.