Helps you put a consistent angle on your knife's cutting edge. STLs are sized for a 50x200x25mm stone and 2mm blade width, see scad if your stone or blade is a different size.Add a drop of oil in the channels to reduce friction and wear. Scad requires tbuser's openscad-bitmap library from http://github.com/tbuser/openscad-bitmap (also linked as ancestor) which is used to write the angle on the car.