Two questions regarding the HP-12C.

1. How does one find the serial number on an old unit? I

have no box.

2. What is the procedure in finding the principal, interest, and future value on a note when the payment is never the same. I posses a note and the payee always pays a different amount on the loan instead of the correct amount. I want to keep up with the amortization schedule

but they never pay the same amount.

Thanks,

Mike Willis

Mike,

1. The serial number should be stamped in the upper right edge of the backside. (A few units are said to have no serial number at all.)

2. Sounds like you will have good use for the 12C, as you will need to recalculate things each time an irregular payment is made. For a given balance and interest rate, the next period requires a certain amount of interest to be paid. If the payment exceeds this interest, the balance is diminished accordingly. If the payment is less than the interest required (not likely, we hope), then the balance must go up by the amount lacking. An amortization schedule does all the calculating for you, so long as the payments are regular in amount and frequency. An irregular payment means that the amount of interest due on the next payment should be recalculated (based on the new balance),and the amortization schedule revised -- you can keep the standard payment the same, but revise the time required to reduce the loan to zero.

Hope this does not muddy the waters. Others on this forum can explain the matter much more clearly.

Cheers, Tom