1) Vibrations in air columns inside closed and open pipes produce standing waves with characteristic frequencies called harmonics or overtones. 2) In closed pipes, only odd harmonics like the fundamental, 1st overtone (3rd harmonic) and 2nd overtone (5th harmonic) are possible. In open pipes, all harmonics including the fundamental, 1st overtone (2nd harmonic) and 2nd overtone (3rd harmonic) are observed. 3) There is an end correction of about 0.3 times the pipe diameter that must be added to the effective pipe length to account for vibrations outside the physical opening. 4) The speed of sound in air can be measured