cathode-ray oscilloscope

The cathode-ray oscilloscope (CRO) is used to measure voltage and its changes over time. This is how the CRO screen would appear measuring AC and DC current.

Instrument used to measure electrical potentials or voltages that vary over time and to display the waveforms of electrical oscillations or signals. Readings are displayed graphically on the screen of a cathode-ray tube.

The CRO is used as a voltmeter with any voltage change shown on screen by an up (positive) or down (negative) movement of a bright dot. This dot is produced by a beam of electrons hitting the phospor layer on the inside of the screen. Over time the dot traces a graph across the screen showing voltage change against time. If voltage remains constant the graph consists of a horizontal line.