Other diatonic harmonicas include octave harmonicas. The chromatic semitone is usually smaller than the diatonic. Initial diatonic harmonica tunings were major key only. Thus common-tone modulations are convenient for modulation by diatonic or chromatic third. Chromatic elements are considered, "elaborations of or substitutions for diatonic scale members". The Greeks analyzed genera using various terms, including diatonic, enharmonic, and chromatic. The distinction between diatonic and chromatic intervals may be also sensitive to context. The song employs the Andalusian cadence or diatonic phrygian tetrachord. Previous jazz forms used harmonic structures, usually cycles of diatonic chords. These two endpoints are not included as regular diatonic tunings. This tuning places the tonic (diatonic) fret on the melody string. They are convenient principally for diatonic or tonal music. The flutina is an early precursor to the diatonic button accordion. They consist of strict diatonic harmony and secondary dominants. Don and Phil, both guitarists, used vocal harmony mostly based on diatonic thirds.