set output 'relative_a.ps' 
set term postscript color enhanced 'Helvtica,18'  
set grid 
set key top right 
set xlabel 'Image number' 
set ylabel 'Instrumental magnitude ' 
set title 'Mag of stars near IY UMa (rel to star A) '
plot [-5:105][4:-1] 'hw_2026.dat' using ($1):($2-$2)             pt 3 ps 0.6 t 'A'  ,    'hw_2026.dat' using ($1):($3-$2) pt 4 ps 0.8 t 'B'  ,    'hw_2026.dat' using ($1):($4-$2) pt 6 ps 0.8 t 'IY'  
set output 
quit 
