You could add another column to indicate which product you're dealing with.
So now your four columns are Product, Previous Inventory, +/-, and New
Inventory.
The previous inventory calculation, starting in B2 could be
=sumif(a$1:a1,a2,c$1:c1). D2 would be =B2+C2. Only change now is that you'd
need to 'prime' this with an initial entry to each item to 'add' the starting
inventory; the sumif function calculates prior inventory by looking backward
and totalling all the +/-'s for that product.

"maintchief" wrote:

My wife is a hotel breakfast hostess. Her boss wants her to keep a weekly
inventory of breakfast food items. In trying to EXCEL it I run into a
problem.
Three columns: Previous Inventory, Additions/Subtractions(+/-), New Inventory.

If I add +/- to Previous Inventory to get New Inventory I get a circular
reference problem.
To avoid this I figure she will have to input Previous Inventory (manually)
from New Inventory and then input +/- to get a 'new' New Inventory. Is there
a way to avoid the double manual input and avoid the circular reference
problem?