Oscilloscopes

Another graphic meter is the oscilloscope. This measures and records quantities that
vary rapidly, at rates of hundreds, thousands, or millions of times per second. It creates
a “graph” by throwing a beam of electrons at a phosphor screen. A cathode-ray tube,
similar to the kind in a television set, is employed.
Oscilloscopes are useful for looking at the shapes of signal waveforms, and also for
measuring peak signal levels (rather than just the effective levels). An oscilloscope can
also be used to approximately measure the frequency of a waveform. The horizontal
scale of an oscilloscope shows time, and the vertical scale shows instantaneous voltage.
An oscilloscope can indirectly measure power or current, by using a known value of resistance
across the input terminals.
Technicians and engineers develop a sense of what a signal waveform should look
like, and then they can often tell, by observing the oscilloscope display, whether or not
the circuit under test is behaving the way it should. This is a subjective kind of
“measurement, “ since it is qualitative as well as quantitative. If a wave shape “looks
wrong,” it might indicate distortion in a circuit, or possibly even betray a burned-out
component someplace.