Glad you got the incrementer part working
from Roger's suggestion (Thanks, Roger !)

Perhaps just a slight refinement to that would be to use
in the starting cell (which may not necessarily be in row 4):

=IF(G4-J4<0,G4-J4,G4-J4+
INDIRECT("'"&PrevSheet()&"'!H"&ROW($A$1:A1)+3))

Then the formula can be copied down to increment nicely as required

The slightly longish incrementer: .. ROW($A$1:A1)+3
will evaluate to: 1 + 3 = 4 in the starting cell
(the "3" is just an arithmetic adjustment to make the start number 4)
and, when copied down, would evaluate to: 5, 6, 7 ...

The expression is also robust against any subsequent row insertions
which may happen above the starting cell compared to using ROW()
(just one way I picked up from here and adopted since)
--
Rgds
Max
xl 97
---
Singapore, GMT+8
xdemechanik
http://savefile.com/projects/236895
--