This drawing instrument is a straight line scribing tool. The inserted sapphire cutting tool has been correctly positioned in it using the small set up block seen to the left. In use, the plastic wheel is run along a ruler scribing a line away from its edge, therefore protecting the tip from damage (they could be easily chipped). A single scribbed line like this could be used in this way to set out a grid or, using double line road cutters, a road map reference panel. When not in use the tips were stored in a protective box open here.