噓~

set xtic auto ;  set ytic auto  
set mxtics 

set xzeroaxis        

   



set grid mxtics     
set border 31 lt 3     

1.dat                 2.dat

1	1		1	1

2	4		2	2

3	9		3	3

4	16		4	4

plot '1.dat' w lp, '2.dat' w lp, "< paste 1.dat 2.dat" u 1"($2-$4) w lp

other setting about tics:
http://gnuplot.sourceforge.net/demo_4.2/tics.html