One who goes to a Tower for training advances through degrees of competence: first Monitor, then levels of Mechanic. Each degree requires an oath to do no harm and not abuse "laran". First, a trainee learns to set up "barriers" to keep his thoughts from being read against his will, and to keep from "broadcasting" his thoughts and feelings. The next stage of training involves learning how to read one's own physiological symptoms such as heartbeat, respiration and body temperature, and (with permission) to read those of others. Once the trainee is proficient at this, he is qualified to "monitor" other "laran" workers to ensure that they are not in danger when working, and takes the Monitor's Oath, with the approval of the members of the Tower. A person who is deemed morally or otherwise unfit to work with "laran" will not be allowed to take the oath and will be expelled from the tower without any more training. This apparently happened to Dyan Ardais.