Standard parallel rule with perspective drawing device

Claim 1

Drafting apparatus of the type comprising a drawing board and a parallel rule slidably resting on the drawing board and having a pair of pulleys rotatably mounted at either end of the rule and a cord having its ends fixed to the drawing board below the respective ends of the rule with the cord extending between the pulleys in a criss-cross manner, wherein and in combination therewith the improvement comprises: a first idler pulley assembly rotatably mounted to the drawing board above one end of the rule, the cord extending around said idler pulley; primary and secondary pulleys rotatably mounted to the drawing board above the other end of the rule, the cord extending tautly around said secondary pulley; drive means for causing said secondary pulley to rotate when said primary pulley rotates; a second idler pulley rotatably mounted to the drawing board below said other end of the rule; an auxiliary cable tautly engaging said primary pulley and said second idler pulley; means for releasably attaching said auxiliary cable to said other end of the rule; and means for releasably clamping the cord to the drawing board; whereby when said auxiliary cable is attached to the rule and the cord is released, the rule moves up and down in an arc centered at a predetermined vanishing point, and when said auxiliary cable is released and the cord is clamped, the rule moves up and down without changing orientation so that parallel lines can be drawn.