Savings annuity calculator with graph help

Settings Remark
Compounding period (N) The compounding period (N) is the number of times the interest is compounded per year. The following compounding periods can be selected:
• daily
360, 364, 365 or 366 times per year
• weekly
52 times per year
• bi-weekly (every two weeks)
26 times per year
• semi-monthly (twice a month)
24 times per year
• monthly
12 times per year
• bi-monthly (every two months)
6 times per year
• quarterly
4 times per year
• semi-annually (twice a year)
2 times per year
• yearly
1 time per year
The compounding periods (N) in one year:
 N = log(((FV * r) / PMT) + 1) and FV = N * T * PMT + I T * log(1 + r)

where:
FV = Future value
R = Nominal interest rate per year (as a decimal, not in percentage)
T = Time period in years
I = Interest amount
N = Number of compounding periods in one year
PMT = Periodic payment amount, paid at the end of each payment period

Note:
r = interest rate per period

For example, if you borrow \$1000 for 2 years at 12% interest compounded quarterly, you must divide the annual interest rate by 4 to obtain the interest rate per period
(r = R / N = 12 / 4 = 3%).