set size 0.5,0.5
set terminal postscript eps "Helvetica" 11
set output 'bd20r2.eps'
set key left top box
set ytics 500
set xtics 200
set xlabel "x"
set ylabel "position"
plot "bd20r2.dat" using 1:2 title "before" with lines, \
 "bd20r2.dat" using 1:3 title "after" with lines