The “Fifth” is the term often used to refer to the mode of vibration that occurs on the Short Axis of a note panel, with the nodal line running along the Long Axis. The term is often used interchangeably with “Harmonic”. In a perfect world, the Fifth would be tuned an octave and fifth above the Fundamental frequency, since this corresponds to (almost) exactly three times the frequency of the Fundamental. Commonly we refer to a “flat Fifth” or “sharp Fifth” depending on what frequency the mode is actually tuned to. This is not the same as the musical term “Flat Fifth”, as in a tuner’s world we might mean the Fifth is tuned 25c flat.