Excel XP on WinXP

First let me say that maybe I just don't understand financial functions,
although I have done amortizations in the past.

I am having trouble understanding what is happening with the NPER function
recently.

Using the NPER function gave me disappointing results for a calulation I was
making. I decided to test the function ( and my use of it) against a known
value-- A current mortgage. Mortgage amt 50,000, rate 6.875% and term of 15
years with a monthly payment of $475.25. I used the formula =NPER(6.88%/12,
475.25, 50000, 0). This returned -82.56, which is a long way from the 180
monthly payments my mortgage is scheduled to include.

There must be an error in my execution of the NPER function, but I can't
seem to see where its at. Or am I totally misunderstanding the purpose of
thsi function.

Any light you can shed on this for me will be greatly appreciated.

Thanks to all participants in the Excel Community