These five tone numbers are then converted to their 1st octave tone numbers: 1, 3, 5. Tone number 8 of the second octave is also included. Then, these four tone numbers are added to harmony numerals which creates four intervals: Unison, Octave, Perfect 5th and Major 3rd. An interval is harmony of two sounds.
Finally, these intervals are illustrated on the guitar fretboard. However, it should be noted that these intervals have the same pattern on a 4, 5 or 6 string bass.