Gnuplot chart for a histogram with error bars

plot.gnuplot

#!/usr/bin/gnuplot
# Output format
set terminal png enhanced font "freesans,16" linewidth 2

# Caption
set key inside top horizontal nobox font ",12"

set xlabel ''                   
set ylabel ''                              
set auto x                   
set xtics rotate by -30 offset -1

set style data histogram
set style fill solid border -1
set style histogram errorbars gap 1 lw 1

set datafile separator ";"
set yrange [0.4:1.4]

set style line 1 lt 2
set style line 2 lt 3
set style line 3 lt 4

# Compute error of a/b
# 1. compute relative errors
# 2. add them together
# 3. convert the result back to absolute (multiply by a/b)
error(a,aerr,b,berr) = ((aerr/a) + (berr/b)) * (a/b)

set title 'Title'                               
set output 'output.png'       
# Note: 'every ::3' starts counting from row 3 onwards, when there is more than  
# one heading row                                                                 
plot 'input.dat' every ::3 using ($2/$3):(error($2,$6,$3,$7)):xtic(1) ls 1 ti 'compute', \    
              '' every ::3 using ($5/$3):(error($5,$9,$2,$7)):xtic(1) ls 2 ti 'prefetch', \    
              '' every ::3 using ($4/$3):(error($4,$8,$2,$7)):xtic(1) ls 3 ti 'fetch'