CD

This must refer to an octave scale of the form b c d e f g a b, consisting of the two tetrachords b-e and e-a, and the tone a-b.

That is to say, the tetrachord b c d e is not written , but : and d  e♭ f g is not , but .

In ancient language, the tetrachord Synmmenn (a-b♭-c-d) takes the place of the tetrachord Diezeugmenn.

Draw the line a b, the major axis, and at a right angle to it the line c d, the minor axis of the figure.

On the centre line A mark two lines a b, c d, representing the pitch of the spring.