Thanks for your response. Unfortunately, it didn't work, and it produced an inaccurate result.
Here's what I did:
PV (PaymentAmount, InterestRate / PaymentsPerPeriod, TotalPayments)
if (InterestRate > 0)
then
$ = (PaymentAmount * InterestRate) / (PaymentsPerPeriod * TotalPayments)
else
$ = ""
endif
The formula is wrong, so it produced the wrong result, and the error appeared for every field except PaymentAmount. Weird.
So, I tried this:
PV (PaymentAmount, InterestRate / PaymentsPerPeriod, TotalPayments)
if (InterestRate > 0)
then
$ = (PV (PaymentAmount, InterestRate / PaymentsPerPeriod, TotalPayments))
else
$ = ""
endif
This produced the right result, but I still received the error message when tabbing out of InterestRate.
As a workaround, I can swap the fields so that PaymentsPerPeriod appears first, which would work fine unless someone manually filled in the InterestRate field first without using the tab function. I just wish I could get a script to work.