Something like a invoice number counter but have to count up to 600 rows.
ie: a1+b1=b1
     a2+b2=b2 etc.

1st counter wil look like= 10(a1)+10(b1)=20(b1)
2nd couner=50(a1)+20(b1)=70(b1)
3d counter=30+70=100 etc.

where "a" changes anb "b" is counter.

Forward thanks.