Notation
Since microtonal intervals are impractical to accurately notate, a simplified musical notation system was adopted in Arabic music at the turn of the 20th century. Starting with a chromatic scale, the Arabic scale is divided into 24 equal quarter tones, where a quarter tone equals half a semitone in a 12 tone equal-tempered scale. In this notation system all notes in a maqam scale are rounded to the nearest quarter tone.
This system of notation is not exact since it eliminates microtonal details, but is very practical because it allows maqam scales to be notated using Western standard notation. Quarter tones can be notated using the half-flat sign or the half-sharp sign . When transcribed with this notation system some maqam scales happen to include quarter tones, while others don't.
In practice, maqams are not performed in all chromatic keys, and are more rigid to transpose than scales in Western music, primarily because of the technical limitations of Arabic instruments. For this reason, half-sharps rarely occur in maqam scales, and the most used half-flats are E, B and less frequently A .
Read more about this topic: Arabian Maqam