AB is usually late to class (no guarentees). Negative numbers mean that he is early (for example -2 would stand for he came 2 minutes early), positive numbers mean that he is late (for example 3 would stand for he came 3 minutes late). The market will round up (if class starts at 11: 00 but he came at 11: 00 and some seconds, he is considered 1 minute late). If he doesn't show up to class or I forget to check the time he comes, market resolves NA. I will not bet on this market.