This is a simple arrangement for drawing lines in correct perspective. It consists in three arms of equal length pivoted together at one end by a screw-clamp. Two pins are inserted in the drawing-hoard, against which two arms of the ruler abut. The angle of these arms and the position of the pins are governed by the distance required for the vanishing point, as the greater the angle, the further the same is removed, and vice versa. Once adjusted, the parts are clamped firmly together, and the lines ruled by the upper side of the arm which rests upon the paper. The arms at an angle are kept in contact with the pins, and the ruling arm is moved up or down the paper.

The Perspective-Ruler