As per Vijaya Malini tantra:
In one of the systems of Kundlini breathing procedure the distance of heart to crown is said to be 36 fingers. Sun form pran arises in the heart and sets in the crown while moon of the apaan arises in the crown and sets in the heart. Thus in this length of 36 fingers all the pran and apaan arise and fall. The change over points where Sun sets and Moon arises (crown of the head) and Moon sets and Sun arises (in the space of heart), are called the Sandhya kaals. The downward flow of pran shakti from crown to heart, represents wasting of seminal flow. More the downward of this shakti or power, more the ignorance of the jeeva. As the pran rises from heart towards head its called the state of a Bhudhyaman, as it represent the rising of the knowledge of the Sun. As it rises more and more, a practitioner is provided with more and more energy or power. When this power is generated to the maximum, the practitioner is called Budh. After generating the full power, when he can control it totally, the practitioner then is called Prabudh. During this state, he reaches the realm of Brahmrandhra. At this point whatever knowledge that has arisen in him, now he can understand that fully. He can understand the tattva. As per the Sahd adhwa Shodhan practice of cleansing of all elements, he is said to be in the space of Vyapini which is also symbolized in the area of head where a brahmin develops a Shikha. This is a very high state during meditation, when the practitioner can feel the spandan and tingling in the space of his shikha. Here an inkling of param tattva is felt. Shabd brahm of the vedantins and Kundlini of Tantriks represent the same thing.
When all samskaras of the mind are annihilated, the practitioner reaches a state which is referred to in scriptures as Jivanmukt as while living in body he is set free. According to the practitioners, the matrikas can be realized in the rise and fall of the breath. Whole of the alphbets of our Hindi language can be divided into 8 groups, namely अ, क, च, ट, त, प, य, and श respectively. While in the gross world the whole day is divided into 8 parts each called a prahar, four prahars of the day and four prahars of the night. For a yogi these eight prahars are passed in just one breath. As the breath rises from the heart to the Brahmrandhra a span of four prahars is completed and when it descends down from Brahmrandhra to the heart, next four prahar period finishes. As it rises from heart ot the brahmrandhra day time elapses and when it descends from Brahmrandhra to Heart night time is passed. In the middle of going up one faces mid-day while in the middle of coming own one faces mid night. Thus palat of the mouth is the point where mid day occurs while going up and mid night occurs while coming down. The above up and down movement during one breath is compared to one month time in the outer world. One half representing Shukla paksh or nights of waxing moon, the other one being the nights of waning moon or Krishna Paksh. The turnover points where day turns to night and noght turns to day is called Sandhya points. At one Purnima or full moon occurs while at the other amavasya or no moon night occurs. Upward movement when the Sun rises from the heart and sets in the Brahmrandhra results in Amavasya there represents Krishnapaksh while downward movement of Apaan in which moon rises representing Shuklapaksha end in poornima in the heart. While going up kalas of the moon decrease while coming down kalas of the moon increase. In the heart where poornima arises, is the point of Panchdashi.
The complete varna mala is called matrika which are the cause of whole creation. Matrika is from root Avart, means circular, that which moves us in the circle of life death continuously is called Matrika. All these matrikas are represented by various alphabets each of which sit on the petals of the six chakras explained by tantra in our physical body.
A yogi realizes all the alphabets in his own breath, experiencing them he realizes. As we inhale we hear the sound of A (आ) and as we move through a distance of 36 fingers upwards a kind of contra\ction occurs at the end and O (उ) sound is generated. Moving from A to O, in the middle E (इ) is generated. Thus we can say that all the three vowels arise while going up in the breath. Now while exhaling with more pressure produced first Aa (आ) is generated in the Brahmrandhra and as we descend and enter heart area, Õ(ऊ) is generated. While descending in the middle ê(ई) is generated. Thus three vowels are more generated in the downward movement of exhaling breath. Thus smaller vowels lie in Krishnapaksh and bigger ones in Shukla paksh. At the end of pran in the Brahmrandhra Bindu(ं) takes form while at the end of the exhale in the heart Visarg(:) takes place.A and E join together to form Ai(ए) on rising breath while Aa and Ei join together to form æ (ऐ) on exhaling breath at 18 finger distance. Mixed swar ऋ and ॠ are generated at crown and forehead respectively. Lri(ऌ) is generated in throat while Lrî(ॡ) is generated in the heart. Sa-kaar arises in the heart while H-kaar being effulgence pervades everywhere. Each of these varnas take 216 pranachars to develop fully thus we can say that all the fifty varnas take 10,800 pran movements. During rising each varna arises at a distance of three fingers while on the descent they arise at distance of 2.25 fingers distance. All the vowels represent Moon and essential for creation. The palat, a point of mid-day while going up and mid night while coming down, is an important point. Dhyan, havan and poojan done at this point provides final emancipation to the spiritual practitioner or sadhak.
As per Shiv swarodaya 12 fingers in front of the nose tip is the space of moon. Heated breath coming from the inside becomes cool as it merges in to this space while cool breath coming here becomes hot as it merges inside in the space of the sun.
The practice of the sadhak is to observe this space of 12 fingers. In this length of 12 fingers all the great powers lie. As the sadhak reduces the length of breath from 12 to 11, one kind of power is achieved by him. As he keeps on reducing the length of the exhaled breath finger by finger, every time a new power manifest in him. When his breath comes to the nose tip, it becomes so subtle that if strand of cotton is placed at the nose tip even that is not agitated by inhale or exhale breath then he achieves the state of Paramhamsa. His dependence on the nature becomes zero and he becomes totally free. He is not affected by the five elements of the nature anymore and does not require any thing to eat or drink. For the details of the power acquired during this 12 finger journey can be seen in the Swarodaya Shastra of Lord Shiva.
Human body has seven main chakras as per tantra namely, Mooladhar1, Swadhishthan2, Manipur3, Anahat4, Vishudhi5, Ajna6 and Sahasrar7. First five represent the five elements of the nature. Manipur in the middle of the body represent the space of jatharagni or digestive fire, in a way space of Sun while our Vishudhi chakra carrying all the vowels represent space of nectar or Moon. The nectar coming from Sahasrar is continuously dripping into the area of the Moon and falls down from there into the space of the Sun in Manipur and thus consumed. The effort of the sadhak is not to let fall into the digestive fire but taste it himself which he does with the help of Vipritakarani mudra. By inverting he raises the Sun above the moon and farces the nectar to return to Vishudi and from there directs it to the source, thus traverses the return journey.