Optional pre-averaging delay correction

[amsrichards]

As mentioned:
Sometimes (a minority of data sets, but not rare) there are very high delays, usually to Cm, for some scans, typically on the phase-ref/target, such that the delay calibration has to be done before channel averaging. Please can we have an optional step near the start to run gaincal 'K' on all calibrators? Ideally just before split, but I do not know whether it should be done before or after hanning/pre-flagging for data with bad rfi (at C-band, no pre-flagging etc. is OK). Then before split applycal should be run to apply the delay for all calibrators to themselves, and for the phase-ref to the target, and split needs to use Corrected.

In terms of diagnostics to decide if this is needed, averaging central ~100 chans of raw data and plotting the data (~30-sec averages to 'see' phase ref) amp v. time may show a drop in amps, usually to Cm and often different for RR and LL. You need to note scan numbers where any jumps come on the phase-ref as the intermediate target scan will have an undefined delay and need flagging. Then plot phase v. channel, phase-ref scan averages in time, central few tens chans, to check that high delay is the problem. Thanks.