Centering:

The compass is set so which its centre lies exactly above the station under consideration. This is achieved through suspending a plumb bob from the centre hook given. If the conical end of plumb bob lie exactly over the station (X is marked over station for accuracy), the compass is considered to be exactly centered. If not, then the legs of the tripod are adjusted in position through moving one leg first and then simultaneously moving other two legs in perpendicular direction to first movement. Several trials can be needed for obtaining the correct centering of the compass. In real life situations, when plumb bob is not available, a little piece of stone or pebble could be taken, by holding this stone by fingers in line of centre of compass and permitting it to drop freely on the station. If the stone falls on the top of peg then centering is correct, or else the adjustment of tripod is completed as explained earlier.