# set terminal pngcairo  transparent enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'contours.4.png'
set bar 1.000000 front
set style circle radius graph 0.02, first 0.00000, 0.00000 
set style ellipse size graph 0.05, 0.03, first 0.00000 angle 0 units xy
set key at screen 1, 0.9, 0 right top vertical Right noreverse enhanced autotitle nobox
set style textbox opaque margins  0.5,  0.5 noborder
unset logscale
set view 60, 30, 0.85, 1.1
set samples 20, 20
set isosamples 21, 21
set contour base
set cntrparam levels discrete -75,-50 ,0 
set style data lines
unset paxis 1 tics
unset paxis 2 tics
unset paxis 3 tics
unset paxis 4 tics
unset paxis 5 tics
unset paxis 6 tics
unset paxis 7 tics
set title "discrete set of contours (at -75, -50, 0)" 
set xlabel "X axis" 
set ylabel "Y axis" 
set zlabel "Z " 
set zlabel  offset character 1, 0, 0 font "" textcolor lt -1 norotate
set paxis 1 range [ * : * ] noreverse nowriteback
set paxis 2 range [ * : * ] noreverse nowriteback
set paxis 3 range [ * : * ] noreverse nowriteback
set paxis 4 range [ * : * ] noreverse nowriteback
set paxis 5 range [ * : * ] noreverse nowriteback
set paxis 6 range [ * : * ] noreverse nowriteback
set paxis 7 range [ * : * ] noreverse nowriteback
set colorbox vertical origin screen 0.9, 0.2, 0 size screen 0.05, 0.6, 0 front  noinvert bdefault
splot x*y