The Sri Chakra or Sri Yantra is one of the most scared images of Hindu tantric iconography. Its worship forms the central aspect of the Sri Vidya tradition, whose practical details are a closely guarded secret.
The central portion of Sri Chakra contains nine major interpenetrating triangles: four pointing up, representing Shiva or the male aspect of divinity, and five pointing down, representing Shakti or the female aspect of divinity. The Sri Chakra represents the body of Sri Vidya - the Mother Goddess upholding the entire cosmos. The bindu is present in the middle of the central downward pointing triangle. Two concentric rings of petals, numbering eight and sixteen, surround the Chakra. The whole diagram is then enclosed in a quadrangular structure, called the Bhupura, which represents the boundaries of the manifest cosmos, with four doors leading out to chaos.
One of the classical texts on this subject is the ''Saundarya Lahari''
of Sri Samkara Bhagavatpada. There are also various commentaries on this work, which shed light on some aspects of Sri Chakra worship. Modern works draw heavily from these old sources. Many books and articles on the web dealing with this subject give erroneous or incomplete details, including, sadly, images of Sri Chakra that are simply wrong. Sri Yantra also has various three dimensional forms, for e.g. the ''Meru''.
Authors also tend to weave many complex theories around the Sanskrit letters and beeja mantras associated with Chakra worship and the significance of the various parts of the diagram. Many minute details vary according to the ''expertise'' of the author.
Any interested novice taking her first step towards Sri Vidya meets with a formidable amount of information, packaged as esoteric knowledge, taking the earnest seeker round in circles. The best way of learning this subject, just like any other form of transcendental knowledge, is through discipleship. However, finding a willing expert in the field is hard.
Drawing the perfect Sri Chakra is a formidable task, nearly impossible using conventional compass-protractor methods. Nearly perfect Yantras can be created with the aid of computers.
One method begins by dividing a circle into ten parallel segments of varying thickness, in order: six, six, five, three, three, four, three, six, six and six units each. It is convenient to draw a circle of radius exactly 24 units, as this will avoid any cumbersome decimals while cutting the circle. It is also useful to draw a diameter exactly perpendicular to these lines. Not all the lines we start with will figure in the final diagram, so it is always advisable to draw very fine lines. Then triangles are drawn connecting the various lines. This traditional method is well suited for drawing relatively small yantras since the minute triangles formed at various points of intersection due to imperfect alignment magnify as the size of the diagram increases.