It consists of two metallic rods (one rod is engraved in mms) supported by cast iron feet with one side levelling screw , provided with 4 metal riders. Two of the sliders have transverse motion and two lens holders, two optical pins. Improved design one meter long.1 meter long : For accurate measurement of focal length of Lenses. Overall Length 1700 mm, Scale length 1500 mm (graduated in millimeters). Improvements have also been made in the designs of the end supports and the carriages to make the whole assembly more stable and easier to handle. One rod covered with Brass graduated pipe.NP