1,The top cover made of aluminium, so the instrument is more durable and firmly. 2,Top-mounted optical peep-sight for quick reference. 3,Compensator lock protects instrument during transport or storage; also acts as a handy compensator checking tool. 4,The metal suspension tapes and advanced pneumatic damper make the compensator more adaptable against vibrations ,jolts, shocks and any environmental changes. 5,The advanced structure supply the friction-braked rotation , and endless horizontal drive with a knob at each side. 6,Horizontal circle can be readout 1?or 1gon directly . 0.3m is the shortest focusing for measurement in confined spaces.