You can check the value of the cells you are summing before going ahead with
the calculation. So you could change the formula:

=Sheet1!A1+Sheet2!A1

to:

=IF(OR(Sheet1!A1<"",Sheet2!A1<""),Sheet1!A1+Shee t2!A1,"")

Hope this helps
Rowan

"Maribel" wrote:

I am summing up cells from two different sheets (1, 2) onto a third. Some of
the cell values on the first two sheets may not have anything in them, yet
when I type in my formula on the 3rd sheet to sum the cells, I get a 0 value.
The project I am working on has values of 0, 1, 2, and 3, so when there is a
missing value I need to know about it (I do not know how to get Excel to do
this - get no value, not even 0 in the results). Yet, right now when there
is a missing value, I get a result of 0, which is confusing since that is one
of the values I am interested in. Any help? Does this make sense?