Instrument of ancient origin, utilized to verify verticle lines. It consists of a cord that is pulled towards the ground by a weight usually in a conic form. In the ancient examples, it was made of iron or copper filled with lead. Along the cord, a metal square is found, with the side equal in diameter to the weight. Resting the metal square transversely on the work, the vertical is determined when the outer edge of the weight is tangent to the work itself.