Why is today's invigilator the same as yesterday's original class?

Educational arrangement. The invigilator is the monitor of the examination room and the only person who can move freely in the examination room. And the examination room is standard for two or three invigilators. The invigilators for two consecutive days are in the same class, which may be a mistake in the arrangement of the Academic Affairs Office or a pure coincidence. Before each exam, the invigilator is organized by the test center, and the invigilator group draws lots randomly, and then three invigilators are randomly sent to the examination room.