Apple Numbers '08 - Manual (Page 257)

Chapter 12 Dictionary of Functions 257
PMT
The PMT function calculates fixed, periodic payments, given the interest rate, number
of periods, present value, future value, and type of payment.
PMT(rate, num-periods, present-value, [future-value], [when-due])
 rate: The interest rate per period.
 num-periods: The number of periods.
 present-value: The present value of the investment.
 future-value: Optional; the future value of the investment or cash value remaining
after final payment. If omitted, future-value is assumed to be 0.
 when-due: Optional; specifies whether payments are made at the beginning or end
of each period:
0 (or omitted) means payments are at the end of each period.
1 means payments are at the beginning of each period.
Notes
To break down a payment into principal and interest components, you can use the
PPMT and IPMT functions.
POISSON
The POISSON function uses the Poisson distribution to calculate the probability that a
specific number of events will occur.
POISSON(events, mean, cumulative)
 events: The number of events (arrivals) for which you want to calculate the
probability.
 mean: The known average rate of events.
 cumulative: Determines whether the reported probability is cumulative:
TRUE calculates the probability that there will be the specified number of arrivals or
fewer (also called the cumulative probability).
FALSE calculates the probability that there will be the specified number of arrivals
(sometimes called the probability mass).
Examples
PMT(10%/12,36,10000,0) returns -$322.67. The return value indicates that a $12,000 purchase minus a
$2,000 down payment (or $10,000) over 36 months at a 10% interest rate requires monthly payments
of $322.67.