Tuning using 'just intonation' is also considered microtonal. Just intonation is the tuning of notes based on exact frequency ratios of notes. For example, with A=440hz, to find a perfect 5th, you would do 440*3/2. Therefore, E=660hz. 12-tet approximates these frequencies to allow for better tuning in all keys, for example, in 12-tet, E=659.225hz.