- Transparent, Perspex/Plastic molded 264 x 20 x 2.7 mm to 3 mm having 3 slots of width 5 mm. at a distance of 0 to 30 mm., next 50 to 200 mm. and again 220 to 250mm.
- Numbering from 0 to 25cm.with mm. markings in it on both sides, all markings and numbering with center line in black colour.