14.9The same physical notes can represent four diminished chords

Take:

B D F A♭

Because every note is equally spaced, the same four piano keys can be interpreted as:

B°7

D°7

F°7

A♭°7

depending on context and spelling.

At the piano, it's literally the same shape.

This means:

Learn one diminished-seven shape and you have four theoretical roots.