$MARK_1 <<EOM
0	0	1
1	0	1
1.5	-1	1
2	-1	1
EOM
set mark 1 $MARK_1 
undefine $MARK_1

# set terminal pngcairo  transparent enhanced font "arial,10" fontscale 1.0 size 600, 400 
# set output 'mark_labels.1.png'
set border 3 front lt black linewidth 1.000 dashtype solid
set style fill   solid 1.00 border rgb "black" 
unset key
set style histogram columnstacked title textcolor lt -1
set style data lines
unset xtics
set ytics border out scale 1,0.5 nomirror norotate  autojustify
set ytics  rangelimit autofreq 
set title "Adjustable height mark used to attach labels" 
set title  offset character 0, 1, 0 font "" textcolor lt -1 norotate
set xrange [ -3.00000 : 5.00000 ] noreverse
set yrange [ 0.00000 : * ] noreverse
set y2range [ 0.00000 : * ] noreverse
set link y2 
set lmargin at screen 0.2
set bmargin at screen 0.15
set rmargin at screen 0.8
set tmargin at screen 0.75
label_ypos(i)  = label_bot + i*label_inc
mark_yscale(i) = $2 - label_ypos(i)
NO_ANIMATION = 1
label_bot = 2.0
label_inc = 1.0
## Last datafile plotted: "$data"
plot newhistogram at -0.5, $data using 3 with histogram,      $data using (0.0):2:(1):(mark_yscale($0)) axes x1y2                     with marks units xy lt black,      $data using (2.0):(label_ypos($0)):(sprintf("%s (%.1f)",strcol(1), $2)) axes x1y2                     with labels offset 0.5 left font ",10"