The power of Yantras to induce resonance is based on the specific form of its appearance. Such a diagram can be composed from one or more geometrical shapes which combine into a precise model representing and transfiguring in essence, at the level of the physical universe, the subtle sphere of force corresponding to the invoked deity. From this point of view we can argue that the Yantra functions similarly to a mantra (sacred word). By resonance, a certain energy from the practitioner's microcosm vibrates on the same wavelength with the corresponding infinite energy present in the macrocosm, energy which is represented in the physical plane by the Yantra. The principle of resonance with any deity, cosmic power, aspect, phenomenon or energy owes its universal applicability to the perfect correspondence existing between the human being (seen as a true microcosm) and the Creation as a whole (macrocosm).

The Yantric Contour
Every Yantra is delimited from the exterior by a line or a group of lines forming its perimeter. These marginal lines have the function to maintain, contain and prevent the loss of the magical forces represented by the core structure of the Yantra, usually the central dot. They also have the function to increase its magical and subtle force.

The core of the Yantra is composed of one or several simple geometrical shapes: dots, lines, triangles, squares, circles and lotuses representing in different ways the subtle energies.

The Dot (bindu)
For example, the dot (• or the bindu) signifies the focalized energy and its intense concentration. It can be evnisaged as a kind of energy deposit which can in turn radiate energy under other forms. The dot is usually surrounded by different surfaces, either a triangle, a hexagon, a circle etc. These forms depend on the characteristic of the deity or aspect represented by the Yantra. In the tantric iconography, the dot is named bindu; in tantra bindu is symbolically considered to be Shiva himself, the source of the whole creation.

The Tiangle (trikona)
The triangle (trikona) is the symbol of Shakti, the feminine energy or aspect of Creation. The triangle pointing down represents the yoni, the feminine sexual organ and the symbol of the supreme source of the Universe, and when the triangle is pointing upwards it signifies intense spiritual aspiration, the sublimation of one's nature into the most subtle planes and the element of fire (Agni Tattva). The fire is always oriented upwards, thus the correlation with the upward triangle - Shiva kona. On the other hand, the downward pointing triangle signifies the element of water which always tends to flown and occupy the lowest possible position. This triangle is known as Shakti kona.

The intersection of two geometric forms (lines, triangles, circles, etc.) represents forces that are even more intense than those generated by the simple forms. Such an interpenetration indicates a high level in the dynamic interaction of the correspondent energies. The empty spaces generated by such combinations are described as very efficient operational fields of the forces emanating from the centeral point of the Yantra. That is why we can very often encounter representations of mantraS in such spaces. Yantra and mantra are complementary aspects of Shiva and their use together is much more efficient than the use of one alone.

The Six Points Star (shatkona)
A typical combination often found in the graphical structure of a Yantra is the superposition of two triangles, one pointing upwards and the other downwards, forming a star with six points (shatkona), also known as David's Star. This form symbolically represents the union of Purusha and Prakriti or Shiva-Shakti, without which there could be no Creation.

The Circle (chakra)
Another simple geometrical shape often used in Yantras is the circle, representing the rotation, a movement closely linked to the shape of spiral which is fundamental in the Macrocosmic evolution. At the same time, the circle represents perfection and the blissful creative void. In the series of the five fundamental elements it represents air (Vayu Tattva).

The Square (bhupura)
Between the simple geometrical elemets that compose Yantras there is also the sqaure (bhupura). The square is usually the exterior limit of the Yantra and symbolically, it represents the element earth (Prithivi Tattva).

Every Yantra starts from the center, often marked by a central dot (bindu) and ends with the outer square. This represents the sense of universal evolution, starting from the subtle and ending with the coarse, starting from "ether" and ending with "earth".

Even tough most of the times Yantras are composed of these simple geometrical shapes, sometimes we encounter other elements such as arrow points, tridents, swords, spikes included in the design of a Yantra with the purpose of representing vectors and directions of action for the Yantric energies.

The Lotus (padma)
The lotus symbol (or its petals) is both a symbol of purity and variety, every lotus petal representing a distinct aspect. The inclusion of a lotus in a Yantra represents freedom from multiple interference with the exterior (purity) and expresses the absolute force of the Supreme Self.

In conclusion, a Yantra is a very complex spiritual instrument in the tantric practice (sadhana). It can calm and focus the activities of the mind, and by its positive auto-suggestion it has a benefic impact on the health and psychic well being of a person.

A Yantra alone represents nothing. Only when it is awakened by mental concentration and meditation will the process of resonance appear and the benefic macrocosmic energies will manifest themselves in the practitioner's microcosm.