LEVELS

        [GREG2\]LEVELS C1 C2 TO C3 BY C4 ...

    sets the contour levels to be C1, C2, C2+C4, C2+2*C4, ..C3, and  so  on,
    using  the same list format as SIC\ command FOR.  The contour levels are
    used to make contour plots of  the  Regular  Grid  array  using  command
    RGMAP.  Up  to  30 contours can be given at a time. Note that it is more
    efficient to use a single RGMAP command with many levels than many RGMAP
    commands with a single level each.

    LEVELS without arguments will display the  contour  levels,  and  LEVELS
    NONE reset the level list.