Thank you gentlemen!  Works like a charm!

Ed (Kentucky, USA)

Hi BigBlueMan!

I should add that where you have arguments for both the PV and FV it
is important that you switch both of their signs. The function is
calculating the PMT that balances the equivalence formula and failure
to switch both signs would throw this out.

Using the switched sign approach is the same as reversing your
"persona". From being a borrower to whom the PV is an amount received,
you become a lender to whom the PV is an amount paid out. Similarly
with the FV argument. From being a borrower who pays out a terminal
payment, you become a lender who receives the terminal payment.

On balance I prefer a sign convention approach but simple negating of
the entire function will do the job.