Activity
HELP
Height of Collimation is the height of the horizontal plane through the telescope. In order to see the staff on the BM the instrument must be higher. To find the Height of Collimation (Instrument Height) add the staff reading to the level of the Bench Mark.
Height of Collimation = BM + staff reading
The survey station is below the horizontal plane through the instrument, so to find reduced level, or ground height, take the staff reading away from Height of Collimation.
Reduced level = Collimation - staff reading
