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.