set ylevs lev1 lev2 ... levN
Allows the user to specify each individual labeled tick mark for the Y-axis.
set ylevs will override the tick mark interval specified with
the set ylint command.
set yaxis to specify
labeled tick marks and also invoke set ylevs, then the tick marks
lev1 ... levN specified with set ylevs will
appear if they fall within the start and end
range specified in the set yaxis command.