fits knows enough about the ATCA and a select group of other telescopes to provide some nominal values for parameters that FITS does not store -- for example a system temperature of 50 K and a system gain of 13 Jy/K are stored with ATCA data. fits also attempts to estimate the integration time. Unfortunately given the information present in a FITS file, this integration time estimate is little better than an educated guess. Task fits gives a message informing you of the values it is using. If you know better values for system temperature, integration time, etc, than those guessed by fits , you may wish to correct the stored values. This is largely so that any noise estimates produced by later tasks are in more meaningful units. You can correct these with the task puthd . Task puthd writes an item into the visibility dataset, which overrides the value of a visibility variable with the same name. The following three parameter boxes show the inputs to puthd to correct the system temperature to 80 K, the system gain to 11 Jy/K and the integration time to 15 seconds.
AIPS FITS files from the ATCA sometimes contain other flaws which MIRIAD \ issues warnings about -- these can usually be safely ignored. These flaws include visibilities with zero weight, incorrect apparent RA and DEC and circular polarisations from the ATCA.