Be able to sell a package of sessions to a client, track those sessions as they are used and have the session package automatically rebilled to the client once those sessions are used. For example, a client buys 3 sessions, for a week's worth of training. Once all 3 sessions are used that week, if they come in all 3 times, then the sessions are automatically sold again, ready to be used for the next week. If they only come in twice in a week, the sessions are rebilled again after the 3rd one is used the next time they come in.