Śulba Sūtra

The Śulba Sūtras ('rules of the cord') are geometric manuals within the Kalpa literature, giving procedures for laying out fire altars of prescribed shapes and areas with cords and pegs. The principal ones are those of Baudhāyana, Āpastamba, Kātyāyana and Mānava, generally dated to the first millennium BCE. Baudhāyana states the relation between the sides and the diagonal of a rectangle and gives an approximation of √2 accurate to five decimal places.