If we have a figure on an horizontal plane, we can draw his perspective image on a vertical plane by this mechanism. A side of rectangular plate moves in a straight path (BQ). On the plate there is a slit TY, perpendicular to BQ and in his point T a rod TP is pivoted.TP is also pivoted on the plane in fixed point P. A point O is fixed on the perpendicular line to BQ through P. A rod OX is pivoted on O . The points A (intersection of TY and OX) and S (intersection of TP and OX) are corresponding in the perspectivity.