band.txt
unset key set ytics set trange[-20:15] set yrange[-2:7] set xrange[0:2.573132] set xtics format " " set xtics add ("M" 0) set xtics add ("R" 0.500000) set xtics add ("G" 1.392341) set xtics add ("X" 1.940458) set xtics add ("R" 2.573132) set parametric plot "band.dat" index 0 using 1:2 with line,\ 0.500000,t with line lt rgb "red",\ 1.392341,t with line lt rgb "red",\ 1.940458,t with line lt rgb "red"