Yantra is basically a diagram representing the astronomical position of the planets over a given date and time. It is considered auspicious in Hindu mythology. These yantras are made up on various objects i.e. Paper, Precious stones, Metal Plates and alloys. It is believed that if we, as humans, follow the basic principal of constantly concentrating on the representation, it helps you build Fortunes, as planets above have their peculiar Gravity which governs basic emotions and karma, derived to attain satisfaction. These yantras are basically made on a particular date and time depending on the prescribed procedures defined under vedas.
Sri Yantra at
http://en.wikipedia.org/wiki/Image:SriYantra_construct.svg
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