Directory billing cycle

Hi, Please could you clarify the settings in the Directory plugin.

It states.....

Use the recurring payments (checkbox)............Fine, easy enough to understand.
Cost of Service Amount to bill for each billing cycle.............Fine, easy enough to understand.
Name of Service ............Fine, easy enough to understand.

However???????

Billing Period The unit of measure for the billing cycle
Billing Frequency Number of billing periods that make up one billing cycle. The combination of billing frequency and billing period must be less than or equal to one year. If the billing period is SemiMonth, the billing frequency must be 1.

How confusing? if billing period is set to 'Month' and frequency set to '1' (your default) does this mean the customer pays just once or once every month?

If I want to set a recurring charge until cancelled, do I need to set the frequency to several hundred?

Surely there is an clearer way to present these options?

Thanks