If for any reason a student leaves the classroom after taking an exam, that student may not re-enter the classroom as long as that exam is still taking place. The student's leaving the classroom will be taken to signify that the student has finished that exam. This includes trips to the bathroom, so plan ahead. The exam will be cumulative, covering the entire course. This includes everything the instructor wrote during class, on the chalkboard or on overhead transparencies.
Re-read especially the class handouts described below.
I can meet with students at other times, too. The handout on The Cosmic Calendar . The handout with the Flowchart on Standard Scientific Method Calculations involving scientific notation, the metric system, and units conversions. Why the Moon has phases, and what times of night the Moon, at different phases, rises and sets. Eye safety, for solar observing.