free grads

set clab

set clab option

Controls contour labeling. The option argument may be one of the following:

on       'fast' contour labels are plotted where the contour lines are horizontal 
off      no contour labels 
forced   an attempt is made to label all contour lines 
format   gives a C-language template for conversion of the contour value to a string 
masked   (version 2.0.a6+) contour lines have gaps for the labels, so rectangles for label background are not drawn; contour labels never overlap.