CLEAN_STOP

      CLEAN_STOP  is  a 2-elements character string that defines the Clean stop-
    ping criterium.

    If CLEAN_STOP is not empty, it supersedes the older  CLEAN_ARES,  CLEAN_FRES
    and CLEAN_NITER variables (and their even older ARES, FRES, NITER historical
    equivalent),  and  even  the CLEAN_NKEEP variable, providing a more flexible
    syntax to specify the stopping criterium.

    The general syntax is
      LET CLEAN_STOP Value [Unit]
      LET CLEAN_STOP   1 Sigma     Indicates stopping at 1 times the noise level
      LET CLEAN_STOP   10 mJy      Indicates stopping at 0.01 Jy/beam
      LET CLEAN_STOP   1  %        Indicates stopping at 0.01 of the peak value
      LET CLEAN_STOP   100 Iterations  Set the max number of iterations to 100
      LET CLEAN_STOP   20 Stop     Indicates convergence is tested over 20 itera
    If no unit is specified, the last specified unit is used instead.  Sub-units
    (mJy, Jy, milliJy, microJy, etc...)  are allowed for convenience.

    CLEAN_STOP  overwrites  the  previously  specified  CLEAN_ARES,  CLEAN_FRES,
    CLEAN_NITER and CLEAN_NKEEP values when (and only when) CLEAN is executed.