Levelling:

The compass is required to be levelled so that the aluminium ring is in horizontal plane and hence free to rotate on pivot. The levelling can be checked by a spirit level or by rolling a pin on compass box. If the round pin does not roll, a level is correct. If not levelled correctly, the level could be adjusted by moving the legs of tripod. Some instruments are provided with a ball and socket arrangement at box base to achieve rapid levelling till the graduated ring moves freely inside the compass box.