The duration of the  breath (ana) establishes the unit of time (laya). The unit of time should be maintained “relatively constant” throughout the practice.

The laya determines:

• the duration of each karaṇa (unit of movement),
• the duration for which a steady posture (āsana) is hold and
• the very pace of the composition (vinyāsa); which varies from person to person.

The shorter is the breath faster is the time-unit (laya). The longer is the breath slower is the time-unit (laya).

Unit of movement (karaṇa-s) is counted in mātrā (count) using ordinal numbers. While the duration for which a posture (āsana) is hold is counted in breath (ana) using cardinal numbers.