#
# change "FIXME" strings to appropriate values
#
* (you can change other things if you like)
#
set terminal png
# FIXME.png is the name of the .png file to contain the plot
set output "FIXME.png"

set xlabel "number of slices"
set ylabel "difference between computed values and M_PI"

set xtics format "%g"
set ytics format "%g"

# FIXME? try with and without this and include it or not depending on
# which way gives a result you think is more meaningful
set logscale 

# FIXME.txt is the name of a file containing output of your program
plot "FIXME.txt" using 1:2 with linespoints title "summing left to right", \
         "FIXME.txt" using 1:3 with linespoints title "summing right to left"