Follicular and luteal phase lengths. â variability of menstrual cycle. attributable to follicular phase. â  Mean cycle length ranges from 27.3 to 30.1 days between ages 20 and 40 years, follicular. phase length is 13-15 days, and luteal phase length is less variable and averages. 13-14 days1-3.
Any sequence of seven successive natural notes, such as C-D-E-F-G-A-B, and any transposition thereof, is a diatonic scale. Piano keyboards are designed to play natural notes, and hence diatonic scales, with their white keys. A diatonic scale can be also described as two tetrachords separated by a whole tone.
Like the familiar major, melodic minor, and harmonic minor scales, the harmonic major scale has the diatonic thirds property, which means that the interval between notes two steps apart (e.g. the second and fourth note, or the third and fifth note, etc..) are separated by a major or minor third, i.e. the interval of three or four semitones.