Erreurs courantes de nivellement

Leveling mistakes can occur when the line-of-sight of the telescope is partially obstructed, leading to incorrect level rod readings.

Mistakes also happen when the surveyor, after relocating the level, takes a reading to the level rod positioned at the wrong turning point. 

Calling out and verifying rod readings using a target can prevent recording incorrect values in field notes. 

To avoid leveling errors, the rod must be held vertically, which is ensured by centering the bubble in the circular levels given on the rod.

The base of the level rod should be clean of any mud and be held on firm ground.

When extending the level rod, ensure the upper part is properly secured, and retract it carefully after taking the reading.

Equal backsight and foresight distances between the level rod and instrument minimize errors. 

Finally, centering the bubble on the level properly, focusing the telescope correctly, checking the telescope's line of sight is parallel to the level tube, and the horizontal cross-hair is perpendicular to the vertical axis of the level, helps avoid errors in leveling.