BEAM_STEP

      BEAM_STEP   Integer

    Number of channels per synthesized beam plane.

    Default  is 0, meaning only 1 beam plane for all channels.  N (>0) indicates
    N consecutive channels will share the same dirty beam.

    A value of -1 can be used to compute the number of channels per  beam  plane
    that ensures that the angular scale does not deviate more than a fraction of
    the  map  cell  at  the  map  edge.  This fraction is controlled by variable
    MAP_PRECIS (default 0.1)