If you format a cell wit =A-b-c to display 15 digits you'll probably find that isn't not exactly zero.

Look here for a possible explanation

http://support.microsoft.com/kb/78113

--
Kind regards,

Niek Otten
Microsoft MVP - Excel

"yhoy" wrote in message ...
| The formula is pretty simple -- if(A-b-c=0, "OK", "ERROR"). Use it on a
| column and around 3-5% gives "ERROR" as result even though the statement is
| true. Urgent help needed!