Remark: Yantra is a Buddhist symbol. It is a nucleaus of the visible and knowable, a linked diagram of lines by means of which visualized energies are concentrated. Yantras may be made in permanent form of many substances. The most important is rock crystal. Its clear colourless substance which can be shaped so as to focus light at its apex in a very good emblem for the all, inclusive substance of fundamental reality just as colourless light includes all the possible colours of light. So crystal can serve as analogy for the substance which includes all substance.