Let us examine the harmonic series for tenor C as played by a cello string. The string vibrates in a complex pattern, producing harmonics that correspond to particular organ stop pitches. This will be explained in the next several screens.
The string vibrates as a whole unit, producing the fundamental, tenor C. The fundamental is the first partial or harmonic, but it is not an overtone.
If you were to play tenor C at the organ and pull an 8-foot stop only, you would hear the fundamental, tenor C.
8' stops are unison-sounding stops; that is, they sound the same note as the key being played.