I have a very simple formula. I am subtracting two values and the result
should be a large number. The only value returned is zero. I have checked
the cell format, I have traced the cell references and I do not find anything
obvious. If I enter the same formula in a different cell, I get the correct
result?!?!?

The cell is not procted, so does anyone have any idea why zero is appearing?

Did you get this sprdsht from another user? It may be that someone has
written a program associated with a certain cell or region of your
spreadsheet, and the program triggers when a certain event occurs- an
event can be entering the cell, leaving the cell, entering data, etc.
Is this a possibility?

To check for this, with your spreadsheet open press ALT-F11. The
Visual Basic editor will appear. In the pane along the left margin of
your screen, select the project name associated with your sprdsht.
Right click the icon associated with your tab, and click View Code.
You'll need to interpret the code to see if if is associated with your
cell and a particular event.