Magnetic Dip:

The magnetic bearing of a survey line at a place is obtained by using a magnetic compass. The needle of this compass will not remain horizontal due to magnetic influence of the earth. That deflection of the needle from the horizontal position is called dip of the needle. Apart from local effects because of presence of magnetic ores in ground or such other localised influences, the magnetic dip of the compass needle will vary from place to place on the surface of earth. It will be horizontal at equator, i.e. zero dip at a place equidistant from both the poles. The deviation from horizontal position will gradually increase as survey lines moves toward the poles. This dip will influence the accurate recording of the bearings. A sliding weight or an aluminium coil can be placed on the higher side of the needle to counter balance this dip and make the needle perfectly horizontal during bearing measurements.