Correct Answer - Option 4 : adjustment of horizontal axis
Concepts:
The following test should be remembered in survey.
1. Azimuth test: It is done to make the line of sight perpendicular to the horizontal axis.
2. Spire test: It is a test carried out to remove error due to non-perpendicularity of the horizontal axis and the vertical axis in surveying Instrument.
3. Cross- Hair ring test: This test is done to make the vertical cross-hair to lie in a plane perpendicular to horizontal axis.
4. Vertical arc test: It is done to make the vertical circle indicate zero when the line of sight is perpendicular to the vertical axis.
