"Josef startled musicians by the accuracy of his ear. Once, at the Metropolitan Opera, he heard a tuning fork supposed to be at 440-A. Josef said it was a shade sharp, and it was."
This is incredibly impressive for two reasons:
- It shows absolute pitch is not necessarily limited solely to semitone identification
- A pure tone from a tuning fork doesn't have any of the characteristic overtones, timbre, etc. that you'd get from an instrument to help identify the sound