This drawing instrument is a double ruling pencil being used here on Astrafoil, a plastic sheet with a matt drawing surface. Each Graphite ‘lead’ is held in place with a thumb wheel screw and shaped into a fine edge using the sandpaper block, seen left. It was important to first close the legs, using the large thumb wheel, in order to check that the leads accurately came together before setting to the required road width. When set up correctly this evenness avoided a ‘twisting’ action when used against parallel rules and, therefore, maintained the correct width. The pencil lines were then inked in with a Graphos pen.