I'm havng a really strange problem with what seems a simple formulas works in one spreadsheet but not the other!! the formula simply adds 2 numbers together in Cell N10

=IF(N8="","",SUM(N8:N9))

However when the same for is used in another spreadsheet and the N9 cell is a minus figure e.g. -1 then the N10 cell just goes blank. There is no conditional formatting in the cell N10 and the formatting is set to minus number with 0 decimal places so I cannot figure out what is going on!!!

Any help on this would be very much apprecaited

Regards

Donal