12 as shown in fig4 and will engage a stop lug 29 when in working position the arm 23 is spring loaded in counterclockwise direction as viewed in fig2 and 3 through the use of a tension coil spring 32 which is attached at one end to a peg or stud 33 mounted on the wall 12a adjacent the outer perimeter of the case but on the interior of the case the second end of spring 32 is attached to an ear on plate 28 that extends laterally out beyond the magnet 31 the spring acts to urge the arm 23 to pivot toward the normal indexed position as shown in fig2 stop peg 29 thus determines and sets this position the spring holds the edge of plate 28 and thus arm 23 against the stop peg 29 note also that the disc 14 is spaced sufficiently out from wall 12a so that the magnet can pass to the inside of the disc in the places where cam surface 26 is recessed inwardly from the outer peripheral edge of the disc 14 assuming that a driving force is being exerted on the disc 14 and cam hub 15 through hub 21 in direction as indicated by the arrow 34 fig2 that is in counterclockwise direction as viewed in fig2 and 3 the engagement of the magnets 25 and 31 will cause the arm 23 to rotate the case 12 and this of course.