In a similar vein, this picture shows two different ends from Lucas magdynos where the face cam is moved by cable. If the assumption is made that they are both used on say, clockwise units, the one on the left would provide 'tight wire' advance where a cable is pulled, compressing a return spring, to pull the cam ring in a clockwise direction. The one on the right would provide 'slack wire' advance where the cable is released, allowing the return spring to rotate the cam ring in the same clockwise direction.