Oscilloscope, electronic instrument that records changes in the voltage of an electric or electronic circuit by a trace of light on the face of a cathode-ray tube (CRT). Oscilloscopes are widely used throughout industry and in scientific laboratories to test and adjust electronic equipment and to follow extremely rapid oscillations in electric voltages; the oscilloscope is capable of following changes that occur within several billionths of a second. Special converters attached to an oscilloscope can convert mechanical vibrations, sound waves, and other forms of oscillatory motion into electrical impulses that can be observed on the face of the CRT.