Click here to purchase the entire book in PDF format. Screen Typically, there is a section on the oscilloscope that lets you control some basic aspects of the display like the Intensity of the beam - a measure of its brightness, the focus and the screen Illumination. In addition, there is also probably a small hole showing the top of a screwdriver potentiometer. If this is labeled, it is called the trace rotation. This controls the horizontal angle of the dot on the screen and shouldn't need to be adjusted very often - once a month maybe.