Leave cell blank when sum is empty

[UBJ]

Okay, I'll try to explain what I'm trying to do.

I have three worksheets, for the sake of the argument let's call them A, B and C. Worksheet C combines the respective cell values of sheet A and B, however many cells in A and B may be empty.

When I try to calculate the sum of two empty cells the result returned is 0. To circumvent this, I could use the following formula:

=IFERROR('Sheet-A!C6+'Sheet-B'!C6,"",('Sheet-A!C6+'Sheet-B'!C6)

However, this would mean that should the values in sheet A and B actually do equal 0 then the cell would remain blank. Somehow I need to differentiate between empty values and a value of zero.

- If the sum refers to two empty cells, the result should be empty
- If the sum =0, the result should be 0

In a nutshell, how can I acheive this?

Thanks!

[martindwilson]

try
=IF(OR(A1="",B1=""),"",A1-B1)
or
possibly
=IF(and(A1="",B1=""),"",A1-B1)

[daddylonglegs]

Assuming you only want to get a sum if both cells contain values try

=IF(COUNT('Sheet-A!C6,'Sheet-B'!C6)=2,'Sheet-A!C6+'Sheet-B'!C6,"")