When the going gets tough, try looking in the operations and service manual for your waveform monitor for the specific information. I will base this discussion on the Videotek TSM-60 waveform monitor. Most waveform monitors have the power and scale illumination controls connected to a single potentiometer located in the upper right corner of the unit. Power is obvious, and scale illumination controls some light bulbs which illuminate the face of the CRT or screen. Our waveform monitors have the graticule etched on the tube face to eliminate parallax errors in measurement.
Some waveform monitors use a graticule plate in front of the tube face.
This control is used to make the beam bright enough to see in the operating environment, but not too bright. As the intensity increases, so does the apparent width of the lines in the display. Focus is obviously adjusted for sharpness, but it's operation might be affected by the intensity control in some units. Focus judgments must be made on horizontal and vertical lines at the same time. Astigmatism is sometimes hidden, sometimes on the rear, but always somewhere.