I think I can help . . maybe
if you have a blank worksheet within the workbook great - if not then add
one (we're going to hide it later). on that sheet type the word "Net
Production" in cell A1 and "Gross Production" in A2. go back to your "main"
sheet click the first/top cell in the "sum" column you want to change and
click DATA and then select VALIDATION. in the validation dropdown menu
select "list", and single click in the area below that (which is where you
specify your list range) - doing so will allow you to click on the sheet that
has the two words you just typed and select that as your range. click ok and
now you should see a drop down menu with your choices.
to NOT see the forumula you are going to have to do your calculations on the
"list sheet" and then go back to your original sheet and link the cells
together - to me that is cumbersome. click on the "list" sheet (to select
it) and click FORMAT, select WORKSHEET and then select HIDE (to get this
sheet out of sight if need be).
go back to your main sheet and a NEW "result" cell put this forumla in
exactly
=IF(a1="Gross Production",A19+B19,D19+E19)
I used the IF function - basically i said if the user chooses GROSS
PRODUCTION from the drop down list then add cells a19 and b19 - if the user
chooses ANYTHING ELSE but that then add cells d19 and e19. you could have
used either one of your choices as long as you adjust the rest of the
function for your choice.
hope this helps
Viva LA PHun