This lesson was taken from one of my Skype classes. One of my students asks a question about stretch and the different amount of stretch that piano tuners put on a piano.

Without measuring interval sizes using beat speeds, all a tuner can do is guess at how much stretch is desirable. Granted, experienced tuners can get better at producing consistent stretch by it takes decades of error, and even then, the degree of accuracy, precision, and speed is probably low compared to what we can do with the A.P.E. Method.