The most common just intonation tuning is called Pythagorean tuning. In Pythagorean tuning, the octave (the interval between two notes that sound twice as high or as low as each other) is divided into 12 equal steps. Each of these steps is called a semitone.
The following table shows the intervals between the notes of the chromatic scale in Pythagorean tuning, expressed as ratios of frequencies:
* C: 1/1
* C♯: 256/243
* D: 9/8
* D♯: 32/27
* E: 5/4
* F: 4/3
* F♯: 45/32
* G: 3/2
* G♯: 512/343
* A: 5/3
* A♯: 6/5
* B: 15/8
As you can see from the table, the intervals between some notes in Pythagorean tuning are not exactly equal. For example, the interval between C and C♯ (called a semitone) is smaller than the interval between D and D♯ (also called a semitone). This is because the intervals in Pythagorean tuning are based on the ratios of small whole numbers, rather than on equal intervals.
The unequal intervals of just intonation can create a more complex and interesting sound than the equal intervals of equal temperament tuning. However, just intonation can also be more difficult to play in tune, as it requires musicians to adjust the pitch of their notes slightly to match the intervals.