Addition of two sinusoidal waves. Addition of two sinusoidal waves is demonstrated on the oscilloscope screen. A rapidly oscillating sinusoidal wave (top trace) is added to a slower wave of greater amplitude (middle trace) and the result is shown by the bottom trace. An oscilloscope is a very versatile electronic instrument that is used to visualize and measure electrical signals changing in time. Here a modern digital oscilloscope by Tektronix (no brand name visible) is shown. Photo Nov 2007.