ABRON' It consists a hollow brass tube 40 cm x 18 cm (length x dia) both sides graduated in millimetres (0 to 15 cm) with Vernier to read 0.05 m. Hollow brass tubes is open at both ends with chuck nut in the middle to which a plane mirror is fixed.Two sold brass cylinders and two hollow brass cylinders, all of length10 cm long are provided so that they are put end to end, they just fill the hollow tube completely. Provided with wall bracket cast Iron shape with chuck nuts and two holes for fixing on the wall