A continuous, cyclic waveform in which the amplitude (or instantaneous voltage) varies according to the sine (a trigonomic function) of the time. It is unique in that it has no overtones whatsoever. Since it contains only the fundamental pitch it gives a smooth rounded tone. Test tones used to calibrate tape machines and other equipment are generally sine waves. In acoustic instruments a flute sometimes has a nearly sinusoidal output. On an oscilloscope a sine wave looks like a symmetrical wavy line.