This keyword specifies the density level for plotting the first (dotted) contour line.
This contour will be plotted at
+ *f*(), where
is the mean density of the section that is being plotted, and
() the corresponding rms deviation (again, not of the whole map but only
of given section). To the best of my knowledge, * GraphEnt* will allow you to give *f* a negative
value, thus allowing you to start contouring from below the mean density level (although I
bet that you could crash either * GraphEnt* or PGPLOT by giving random values to this
parameter). Default is 0.0 (ie, first contour at the mean density).

NMG, Nov 2002