When I saw the article title that's what I expected it to be about. Then I saw your comment and thought "oh, it's going to be about the subtleties of different

When I saw the article title that's what I expected it to be about. Then I saw your comment and thought "oh, it's going to be about the subtleties of different temperaments and how you get to choose which intervals are how far off from sounding right". Turns out it's actually telling you that there are 12 semitones per octave, all representing the same ratio of frequencies. Ah well.