De institutione musica I.18: Diatessaron a diapente tono distare.
Again, the diapente consonance is a consonance of five notes, four intervals, of three tones and a lesser semitone. Let the same number 192 be set down, and let its sesquialter be taken, which makes the diapente consonance with it. Let it be the number 288. Then between these and the previously found 192 let these numbers be placed in the middle: 216, 243, 256; and let the description be formed thus: 192, 216, 243, 256, 288. In the description above, 192 and 256 were shown to contain two tones and a semitone. There remains the comparison of 256 to 288, which is sesquioctave, that is, a tone, and their difference is 32, which is the eighth part of 256. So the diapente consonance has been shown to consist of three tones and a semitone. But a little earlier the diatessaron consonance extended from the numbers 192 to 256. Now the diapente extends from the same 192 to 288. The diatessaron consonance is therefore exceeded by the diapente by the proportion contained between the numbers 256 and 288, which is a tone. The diatessaron symphony is therefore surpassed by the diapente by a tone.