A levelling head has three distinctive functions. They are to support main part of instrument, to attach odolite to tripod and to provide a mean for levelling odolite.

Theodolites are classified into two types. They are transit odolites and non ? transit odolites.

The method of observation includes direct method, used when instrument isn?t possible to set over station and reciprocal method, where two instrument stations are used.

Since more amount of diagrammatic explanation is involved in Graphical and Axis methods, those are able to explain in a brief manner.

The personal errors may be due to errors in manipulation, errors in sighting and reading. Inaccurate levelling comes under errors in manipulation.

Latitude and departure co-ordinates of any point with reference to preceding point are equal to latitude and departure of line joining preceding point to point under consideration. Such co-ordinates are known as consecutive co-ordinates or dependent co-ordinates.

In order to nullify closing error, algebraic sum of latitudes and algebraic sum of departures must be equal to zero, which is necessary for obtaining total traverse area.

Instrumental errors are due to imperfect adjustment of an instrument, structural defects in instrument and imperfections due to wear.

If e is closing error in bearing, and N is number of sides of traverse, n correction applied to bearing of sides will be
Correction to first bearing = e/N
Correction to first bearing = 2e/N
And so on to last bearing = Ne/N = e.

The total latitude and departure of any point with respect to a common origin is known as independent co-ordinate. The independent co-ordinates of any point may be obtained by adding algebraically latitudes and departure of lines between point and origin.