the flow in the sushumna. When the steadiness is disturbed the breath will be diverted to the right or left nostril. 

Use of Nadis  

Sleeping  
While sleeping on the left side the Pingala nadi functions and ida is given rest. If Ida flows while sleeping it will cause disturbed sleep and may be dreaming. Hita nadi in which the mind rests on its way to deep sleep is slightly to the left and should not be disturbed by a flow in the Ida. With Hita nadi disturbed dreams result. Therefore, one should always sleep on the left side resulting in sound sleep and ideal digestion. 

Activities  
All activities that are of a permanent nature and ensures well being for all should be performed when ida flows. Entering a new way of life, wearing new clothes or ornaments, buying house or property, entering a new house for occupation, investing money, starting spiritual studies, traveling, cultivation, marriage etc. 
Actions that are transitory or needs physical energy is performed when Pingala flows. While eating or taking bath Pingala should function. 

Tattvas or the Elements  
The manifested universe is created out of a combination of the three gunas (sattva, rajas, and tamas) and the five elements ( earth, water, fire, air and space). 
With every act of inhalation or exhalation there is a rise and fall of the tattvas. A knowledge of the flow of breath with special understanding of the movement of the tattvas lead to wisdom. Starting from the highest Satya loka to this mundane Bhu loka everything is made of the three gunas and the five tattvas. There are various ways by which one can know the tattva that rises at a particular time in one of the nadis. As these tattvas govern our life and activities a knowledge of the same is essential. When we are able to know the tattva that is flowing at a particular time we can beneficially perform actions that are favored by the tattva. 

Knowing tattva by color  
Sit in a meditative asana. Perform jyoti mudra (See hatha yoga lesson on mudras). Concentrate at the eyebrow center and observe the color pattern.

Knowing tattva by shape
Hold a clean mirror at a distance of six inches from the nostrils, intersecting the flow of breath. Because of the warmth of the exhaled air there will be a dew like formation on the mirror with definite shapes.