Musicians and teachers refer to these in-between notes as quarter tones, using "half-flat" or "half-sharp" as a designation for the in-between flats and sharps, for ease of nomenclature. Performance and teaching of the exact values of intonation in each jins or maqam is usually done by ear. It should also be added, in reference to Habib Hassan Touma's comment above, that these quarter tones are not used everywhere in the maqamat: in practice, Arabic music does not modulate to 12 different tonic areas like the Well-Tempered Klavier. The most commonly used quarter tones are on E (between E and E), A, B, D, F (between F and F), and C.