Notation
Mertebe
The number that shows the time unit of an usul, that is, the denominator of the time signature: the mertebe is 4 in the 28/4 form of Devr-i Kebir and 8 in its 28/8 form; it is 8 in the 9/8 Aksak and 4 in the 9/4 Ağır Aksak. The same usul can be slowed down or sped up by writing it with a different mertebe.