button 28 will cause element 70 to move downward along with reciprocating rod 62 which is guided by holes 64 and 66 when button 28 is released the force of spring 68 will return rod 62 and element 70 to their original positions with continuing reference to fig8 and 9 sub chassis 46 is provided with slots 72 and 74 through which shaft 76 extends gear 78 is fixedly attached to shaft 76 and is located within sub chassis 46 where it is positioned to engage rack of teeth 80 which are molded into the plastic from which element 70 is made it will be apparent that when button 28 is depressed and element 70 moves downward shaft 76 will be moved to the bottom of slots 72 and 74 and rotated by the action of teeth 80 on gear 78 when button 28 is released element 70 will be restored to its former position and will move shaft 76 to the tops of slots 72 and 74 element 70 is provided with pegs 82 which impinge upon shaft 76 when button 28 is depressed so as to prevent rod 62 from moving too far pegs 84 are also provided on element 70 to hold shaft 76 at the tops of slots 72 and 74 when button 28 is in its at rest position gear 84 is fixedly attached to shaft 76 and is located outside of sub chassis 46.