The air traffic controller at the airport tower has a small rectangular box with something written in it, and then slides from one end to the other. What is it?

Progress sheet, used to record flight dynamics. For example, if you issue a landing clearance to an aircraft, mark it on the progress sheet, and then slide it to the next control seat, then that person will issue an instruction to leave the runway, and then someone will issue an instruction to taxi into the parking bay.

Of course, this is usually done by a controller. The process sheet is used to record the dynamics of an aircraft so that the controller can direct the aircraft. An aircraft is a small box, and different boxes represent different aircraft. This way you can see the status of the aircraft under your control at a glance, making it easier for you to issue instructions and avoid conflicts. At the same time, the process sheet records your control process, so that if there is an accident or the like in the future, it is easy to find out whether the cause of the accident is your controller's mistake. Adding the process sheet correctly is also a kind of protection for the controller to avoid accidents. necessary responsibilities.