It consists of a hollow cylindrical brass
tube open at both ends provided with a small chuck (torsion head) in the middle
of which is fixed a plane mirror. The length of the hollow brass tube is 40 cm,
diameter 18 cm and graduated with scale divided in millimeters on both sides
from 0 to 15 cm and with Vernier to read 0.05 mm. Two solid brass cylinders and
two hollow brass cylinders, all of length 10 cm long are provided as that when
place end to end they fill the hollow tube completely. Supplied with superior
quality clamp.
