14.1First, the three diminished-type chords

Let’s use B.

B°

Diminished triad:

B D F

= си ре фа

Formula:

1 ♭3 ♭5

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Bø7 or Bm7♭5

Half-diminished seventh:

B D F A

Formula:

1 ♭3 ♭5 ♭7

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B°7

Fully diminished seventh:

B D F A♭

Formula:

1 ♭3 ♭5 ♭♭7

That last note is theoretically a diminished seventh above B.

So:

° = diminished triad ø7 = half-diminished seventh °7 = fully diminished seventh

These are different chords.