## 3.3. Observing

Once setting up is complete, observations proper can start. Observations need to include calibration data, including data for flux, bandpass, polarisation and gain calibration.

### 3.3.1. Calibration

It is important that sufficient calibration data is taken to characterise the array. This means taking flux and bandpass calibration data for all observations, and leakage calibration data for polarisation observations.

This does not have to be done at the start of the observation, but should be done at some point during the observing session. If appropriate calibration sources are not above the horizon during the observing session, contact the scheduler (Phil Edwards) to discuss options.

For cm and 15mm observations, PKS1934-638 is the appropriate flux calibrator and can usually be used as a bandpass calibrator too (although spectral line observations at 15mm will ordinarily require a stronger source). For mm observations, a planet is needed for flux calibration (PKS1934-638 can also be used in the 7mm band), and a strong source (e.g. PKS1921-293 or PKS1253-055) is required to calibrate the bandpass.