FUNDAMENTALS OF SURVEYING : Temporary adjustments/ or station adjustments

Temporary adjustments/ or station adjustments

Made at every instrument setting and preparatory to taking observations with the instrument.

1)   Setting over the station.

Includes a) centering ofthe optional plummet is used for centering instrument over the station mark by a plumb bob or by optical plummet. B) Approximate leveling by tripod legs

2)   Leveling up: Accurate leveling is done by using foot screws with reference to plate levels or level tube

3)   Elimination ofparallax

 Parallax is the condition arising when the image formed by objective is not in the plane ofcross hairs.

 Parallax can be eliminated in following two steps,

1)   By focusing the eye piece for distinct vision of cross hairs

Point the telescope towards the sky or hold a sheet of white paper in front of the objective and move eyepiece in or out till the cross hairs are seen sharp and distinct.

2)   By focusing the objective: to bring the image of the object in the plane of cross hairs. The telescope is now directed towards the object to be sighted and focusing screw is turned till the image appears clear and sharp.