It doesn't matter which one you buy, they are all pretty much the same. Dr. Mehler tries to stick to a set format in class. He allows students to come in up to ten minutes late. But just because the lecture doesn't start until ten minutes after the hour, the class itself usually starts on time. Those first ten minutes are very valuable.
Students can ask any questions they have at that time.
Once Dr. Mehler closes the door and begins his lecture, he doesn't allow late comers to enter the room. So if you are more than ten minutes late and the door is closed, please don't be rude and enter the class. Just go home. You will have an absence for that day. Dr. Mehler always begins the lecture portion of the class asking if there are any questions.