The interest rate define two data: the percentage and number of days in which the percentage of realized !
The program you use, when you know the interest rate determined for a number of data, and you are interested in what is the rate for a second number of days. Example: you have an interest rate that is realized in 30 days, you are interested in this amount in 365 days. From under a IR1 – % put 1, from under a IR1 – days 30, and from under IR2 – days 365.
IR – interest rate