I am using Office 2007.

I need a formula subtracting one time from another that can produce a
negative amount. The cells are formatted custom h:mm.

For instance Cell A1=6:30 Cell B1=6:45

If you subtract 6:45 from 6:30 I need a result of -0:15 (negative)

All I get is #########

Any help would be greatly appreciated.

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bob