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Phase cal tone extraction is soon to be added to DiFX2.0. All of the hooks are already in place in the control file formats. The following assumptions are explicitly made:
DiFX2.0 will write out the phase cal values in a format very similar to that written by the hardware correlator. This allows the computed phase cal values to be picked up by difx2fits.
A phase cal record will be produced for every integration period. For short integration periods this will result in a lot of phase cal data, but still much less than the visibility data. Phase cal records will be averaged to a desired interval in difx2fits.