It is my opinion that the more pure intervals that are in a stretch, the better the stretch sounds.

It's a fact that the number of pure intervals possible depends on the inharmonicity of the piano you are tuning, and the choices you make when tuning certain intervals.

The following diagrams show how the 6:3 size determines how we can tune the P12 and P19.

"If the 6:3 is tuned pure, then the P12 and the P19 will be the same size."

"It is possible and desirable to tune pure P12 and pure P19"