Ita in tribus generibus tetrachorda ex duobus tonis et hemitonio sunt peraequata, sed ipsa cum separatim  uniuscuiusque generis finibus considerantur, dissimilem habent intervallorum designationem.
Thus in the three scales the tetrachords are equivalent to two tones and a half, but when they are considered separately within the limits of each scale, they vary in the arrangement of the intervals.
final_alignments\Vitruvius_Architecture_Book_5.json