Documentation on qvack

Task: qvack
Purpose: Flag after change to observing setup
Categories: calibration

        Qvack is a Miriad task to flag data for a number of integrations
        after the observing setup has been changed. This is used to
        flag data that is suspect because the instrument had not settled
        correctly after the change in the setup. The data are assumed to
        be in time order.

Key: vis
        Input visibility data file. No default.

Key: select
        Standard uv data selection. Default is to select all data.

Key: interval
        The time interval, in minutes, after a change in the setup, for 
        which the data are flagged. Default is 0.1, which flags for 
        the first 6 seconds after a switch.

Key: force
        The time interval, in minutes, which indicates the amount of time 
        that should ellapse before forcing a (virtual) setup change.
        Thus you can QVACK on data that has distinct scans but no actual 
        change in observing setup.  Note that this means the first 
        INTERVAL amount of data is always flagged. The MODE option is 
        not needed, nor is it used if you set FORCE
        Defaults to no forced setup change.

Key: mode
        This determines what changes in setup cause flagging. Several
        values can be given, separated by commas, Minimum match is used.

        Possible values are:
          "frequency"    A change in the frequency setup. Do not use this
                         option if Doppler tracking is used.
          "source"       A change in the source observed.
          "mosaic"       A change in the observing centre of a mosaiced
                         observation.