Quantity-based RMR is a database setting that you can turn on and off. Normally, the system sets the quantity based on the number of months being billed for. Which means 1 month of RMR is normally considered a quantity of 1. Quantity-based RMR allows you to select a different monthly quantity.
For example, what would have been a quantity of one month at a rate of $30.00 for a monthly cycle total amount of $30.00, could instead become a quantity of 2 for one month of service at a rate of $15.00 for a monthly cycle total of $30.00. To extend the example for clarity, this means that a customer who is billed quarterly at a quantity of 2 and a rate of $15.00 would receive an invoice for a quantity of 6, and a rate of $15.00 for a total of $90.00.
Turning the feature on causes new fields to appear in the RMR add/edit screen so that you can enter the quantity and rate as needed. When invoices print, they use the quantity you have entered. If you know what quantity you want and how much you want billed monthly, but don't want to do the math, the system also lets you enter the total amount and the quantity, and then it will set the rate for you based on these.