The direction of a point or line is defined by the horizontal and / or vertical angle with respect to a reference. For horizontal angle, magnetic meridian, Geographic meridian etc are used as reference. To interior angle, deflection angle, angle to the right etc are used to designate the horizontal direction. Zenith and / or vertical angles are used to designate vertical direction. Theodolite is the most versatile instrument used for measurements of direction. A permanently adjusted theodolite is to be used in the field. But, for each setup it must be in temporary adjustment. However, measurements are usually fraught with errors which must be minimised by applying appropriate correction and taking suitable measures.

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