I refer to the highly informative link below:

http://j-walk.com/ss//excel/usertips/tip080.htm

I am trying to develop a VBA function procedure that will run along a
row of 12 cells (one for each month of the year) and perform a simple
calculation and enter the result of that calculation in the cell where
the VBA function is called from. There is only ever one value per row
(as the rest of the cells in that row are always blank), so once it
has found the only non-blank value in that row then the operation can
cease searching that row.

You can see from the following formula (thanks to the above link) what
I am trying to achieve:

=IF(Criteria1,Criteria1,Criteria2)

Where Criteria 1 is:

=IF(ISNUMBER(ºñ!I10),(ºñ!I$8*ºñ!I$7)-ºñ!I10,IF(ISNUMBER(ºñ!K10),(ºñ!K$8*ºñ!K
$7)-ºñ!K10,IF(ISNUMBER(ºñ!M10),(ºñ!M$8*ºñ!M$7)-ºñ!M10,IF(ISNUMBER(ºñ!O10),(ºñ!
O$8*ºñ!O$7)-ºñ!O10,IF(ISNUMBER(ºñ!Q10),(ºñ!Q$8*ºñ!Q$7)-ºñ!Q10,IF(ISNUMBER(ºñ!
S10),(ºñ!S$8*ºñ!S$7)-ºñ!S10,""))))))

Where Criteria 2 is:

=IF(ISNUMBER(ºñ!U10),(ºñ!U$8*ºñ!U$7)-ºñ!U10,IF(ISNUMBER(ºñ!W10),(ºñ!W$8*ºñ!W
$7)-ºñ!W10,IF(ISNUMBER(ºñ!Y10),(ºñ!Y$8*ºñ!Y$7)-ºñ!Y10,IF(ISNUMBER(ºñ!AA10),
(ºñ!AA$8*ºñ!AA$7)-ºñ!AA10,IF(ISNUMBER(ºñ!AC10),(ºñ!AC$8*ºñ!AC$7)-ºñ!
AC10,IF(ISNUMBER(ºñ!AE10),(ºñ!AE$8*ºñ!AE$7)-ºñ!AE10,""))))))

Can someone please help get me started with a VBA function procedure
that will do the same thing as this long formula¨C please!?!?

Many thanks!