You bid for long or short call. I am B for this month but will bid and should hold A next month since I don't live in IAH and can sit A from home. Long call-A reserves get a 9 hr call out but are the first to get assigned a trip. B reserves get a 2 hr call out and may not get used. Great if you live in base with B reserves. Also, as an A reserves you get to pick up a trip in open time before the B guys do if you see a trip that you really want. A reserves get a 72 hour pay guarantee and B gets 76 hrs. By 1500 the day before, you will know if you are assigned a trip for the next day or not.