I've created a custom function in Excel 2003 to meet a need that's too
complicated to be feasible in a formula. When I initially create the formula
that references my function, the cell containing the formula calculates
correctly. However, when the underlying data changes, the output of the
formula does not change. Manually triggering a recalc of the worksheet via
F9, CNTL+SHIFT+ALT+F9, etc. don't update the result either. I know that the
formula is not recalcing, because I've got a breakpoint in my function, and
the VBA is not being called. The only time that the VBA executes is when a
formula that calls the function is first created.

Is there something special about recalculating cells containing custom
functions that affects how they recalculate? Is there something else I need
to be doing?

Thanks,
Mark