The word oscilloscope has evolved to described a variety of electronic instruments used to observer, measure, or record transient physical phenomenon and present the results in graphical form. A cathode ray oscilloscope (CRO) which uses a cathode ray tube (CTR), is very useful and versatile laboratory instrument for measurement, display and analysis of waveforms and other phenomenon in electrical and electronic circuits. The CRO allows the amplitude of electrical signals such a voltage, current, power etc. to be displayed primarily as a function of time. It produces a two dimensional graph with the voltage presented at an input terminal plotted on the vertical axis and time plotted on the horizontal axis.

Usually the graphs appear as an illuminated trace on the visual (TV) screen of the cathode Ray tube (CRT) and is used to construct a useful model or representation of how the instantaneous magnitude of some quantity varies during a particular time interval. A beam of electron striking a fluorescent (TV) screen produces the luminous spot. The quantity measured is often a changing voltage in an electronic current, acceleration, light intensity, frequency, etc. which has been changed into a voltage by suitable transducer. The time interval over which the phenomenon is graphed may vary over orders of magnitude, allowing measurements which proceed too quickly to be observed directly with the human senses. The measured quantities can be uniformly repeating or essentially not-recurring.

The most useful oscilloscopes have multiple input channels so that simultaneous observation of multiple phenomenon is possible, allowing measurement of the time relationships of related events. With the aid of oscilloscope, rapidly time varying quantities are captured as a static image and can be preserved as a photograph or on paper with a plotter or printer. The record can be transferred into memory of a digital computer to be persevered or analyzed.

The general purpose oscilloscopes are classified as analog oscilloscopes and digital oscilloscopes. Each type has special applications in which it is superior, but many measurements could be performed satisfactorily with either.