Cntrlabel

Syntax:
     set cntrlabel {format "format"} {font "font"}
     set cntrlabel {start <int>} {interval <int>}
     set contrlabel onecolor

set cntrlabel controls the labeling of contours, either in the key (default) or on the plot itself in the case of splot ... with labels. In the latter case labels are placed along each contour line according to the pointinterval or pointnumber property of the label descriptor. By default a label is placed on the 5th line segment making up the contour line and repeated every 20th segment. These defaults are equivalent to

     set cntrlabel start 5 interval 20
They can be changed either via the set cntrlabel command or by specifying the interval in the splot command itself
     set contours; splot $FOO with labels point pointinterval -1
Setting the interval to a negative value means that the label appear only once per contour line. However if set samples or set isosamples is large then many contour lines may be created, each with a single label.

A contour label is placed in the plot key for each linetype used. By default each contour level is given its own linetype, so a separate label appears for each. The command set cntrlabel onecolor causes all contours to be drawn using the same linetype, so only one label appears in the plot key. This command replaces an older command unset clabel.