In anoscilloscope a beam of electrons (1) emitted by a cathode (2) goes through a focussing area (3) where electromagnetic fields (4) direct the beam onto the fluorescent screen that the user sees.

When the device is used as a scientific instrument, there is usually a magnetic field that makes the beam scan the screen horizontally, while the electric signal registered by the machine produces vertical deflections. The following visual illustrates this process: .

The vertical signal does not necessarily have to be a sawtooth or sine wave. The user can have signals that come from microphones, voltmeters, photometers, etc. This makes the oscilloscope one of the most versatile scientific tools. The workings of an oscilloscope from the users point of view can be seen in the following visual.