Freeing the Needle and Damping:

Freeing the Needle

The magnetic needle has to rotate freely over the pivot to get accurate measurement of bearing of the survey line. Tap the compass box after the needle has come to rest. This helps within overcoming the pivot friction, if any. The cover glass may also have gathered static electric charge, when rubbed with cloth while dusting and thus attract and jam the magnetic needle of compass. The glass has to be discharged by applying moist finger on its surface.

Damping

The vibration of compass needle is damped by gently pressing the braking knob. To reduce vibrations and to minimize wear and tear of pivot point, the needle shall be released only when the compass is aligned approximately in the direction of magnetic meridian at site.

It is always advisable to take duplicate reading of the needle for each bearing measurements. The compass is rotated to displace the needle after noting down the first reading Readjust the needle before taking the duplicate reading. This decrease observational errors.