We bill in seconds, do I specify a rate per minute or per second?

This depends on a few things:

1. The quote given to the client.
2. The conversion rule of the product.

If you provide a price to your clients in minutes, then you will setup your rate per minute. If your data is collected in seconds, the seconds will be accumulated for the period, converted to minutes and then multiplied by the rate. For this scenario your conversion rule will be set to "Seconds to Mintues". If your data is collected n minutes, the minutes will be summed together and multiplied by the rate per minute. For this scenario your conversion rule will be set to "Each to Each".

If you provide a price to your clients in minutes, then you will setup your rate per second. If your data is collected in seconds, the seconds will be accumulated for the period, and then multiplied by the rate. For this scenario your conversion rule will be set to "Each to Each". Data is not converted from minutes to seconds.

Refer to docs.varibill.com for more information on conversion rules of products and billing data types of selling prices.