Collimation Error and Two Peg Test

Master Farm Structure and Surveying – Notes, Case Studies & Practical Insights – with Rahul

Collimation Error and Two Peg Test

The Two Peg Test helps determine and correct collimation errors, which occur when the line of collimation is not parallel to the bubble tube’s axis.

Procedure:

Place two pegs (A and B) at a known distance.
Set up the level at the midpoint (C), take staff readings, and shift the level to a new point (D).
Compare the true difference in elevation with the apparent difference.

If the differences do not match, calculate the correction needed for the instrument’s collimation error.
Adjust the readings based on whether the line of sight is inclined upwards or downwards.