Principle of the Automatic Level
The aim of this tutorial is to describe the basic principle of an automatic level.
Principle of levelling.
The level is an optical instrument that provides a height reference. This reference is a horizontal plane through the axis of the telescope, known as the "Height of Collimation".
Once the height of collimation (or instrument height) has been measured the height of other stations can be found by measuring from this plane with a staff.
The height of collimation is found by taking a backsight to a staff placed on a bench mark. The staff reading is added to the bench mark value to obtain the height of collimation.
Once the height of collimation has been found ground height at any spot below this plane can be found by observing the staff and subtracting the staff reading from the height of collimation.
Now check your knowledge: