These notes are given simple names, namely A, B, C, D, E, F, G
in Anglo-American nomenclature. The way in which the diatonic
scale in constructed insures that it is made up of five equal large
intervals and two equal small intervals. Each large interval
corresponds to going up two fifths and down an octave; thus,
e.g., the interval from G to A is identical to the interval from
C to D because in either case one gets from the first note to the
second by going up two fifths and down one octave. The two small
intervals involve the notes at the extreme ends of this series of
fifths---the interval down from F, which is at the bottom end of
the series of fifths, and the interval up from B, which is at the
top end of the series of fifths; they are equal because one gets from
F to E the same way as from C to B---up seven fifths and down four octaves: