Some observations:
1. Do you mean: =SUM(G3:I3) instead of =SUM(G3-I3) ?
2. Press F9 - does it compute properly ? If so, then the calc mode was on
manual. To check / change calc mode: Click Tools Options Calculation tab
3. Is the formula cell formatted as text ? Check / change to either General
or Number via: Click Format Cells Number tab, then re-enter the formula.

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Rgds
Max
xl 97
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Singapore, GMT+8
xdemechanik
http://savefile.com/projects/236895
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"Lollycat" wrote in message
...
I have the cells formatted for numbers and the formula is too simple to
mess
up but it simply won't calculate! What am I doing wrong?

Thank you in advance.