A system of tuning in which the* diatonic comma* is divided equally between the twelve *half-steps* of the *octave*. All the half-steps are equal in size and are exactly one-twelfth of an octave, spanning a frequency ratio of :

, or about 6%, or 1:1.059. In equal temperament, all the *intervals* are the same regardless of the* key* in which one is playing, and none except the octave is perfectly tuned. This makes it very easy to modulate from one key to another, although the keys lose their individuality because they all have equal* intervals*. The result is that the fourth and fifths are within 0.001% of just intervals, however the thirds are about 0.01% away from pure thirds which produce audible beats, the thirds in all keys being equally bad.

See *temperament*, *syntonic comma*, *diatonic comma*.