Enter your gnuplot script (Tutorial) here:
# Plotshare Template for Linear Fitting of experimental data
# Fill in x- and y-labels, as well as the plot functionfunctions and plot parameters
set pointsize 2
set xlabel ''
set ylabel ''
f(x) = m*x+n
fit f(x) ExtData1 using 1:2 via m,n
plot ExtData1 title "Measured Data", f(x) title "Linear fit"