Final answer:
A tetrachord must be within the interval of a perfect fourth. On a guitar, harmonic frequencies relate to the fundamental frequency and are a result of the string's division into segments.
Step-by-step explanation:
The notes in a tetrachord must be bound within the interval of a perfect fourth. In musical theory, a tetrachord is a series of four pitches that are within the range of a perfect fourth. For instance, in a standard tuned guitar, the first four frets of any string will give the notes of a tetrachord. On a guitar string, when a string is divided into segments that are fractions of the string's length, these segments can vibrate independently to produce harmonic frequencies. The fundamental frequency is produced when the string vibrates as a whole, between the two fixed ends.