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  LEV-
    ELS NONE reset the level list.