Personal errors in levelling

Personal errors are mistakes or errors caused by the surveyor or the staff holder, not by the instrument or the weather.

• Bubble not centred exactly at the time of the reading, or the instrument not levelled properly.
• Staff not held vertical (leaning forward or backward), so the reading is too high; it can be avoided by waving the staff and taking the least reading or by using a staff bubble.
• Parallax from improper focusing of the eyepiece and the objective.
• Wrong reading of the staff (e.g. reading a wrong metre/decimetre figure, or reading an inverted staff), and wrong booking in the field book.
• Staff not held on the same point at the change point when the level is shifted.
• Moving the staff or the tripod during observations.
• Calculation mistakes while reducing the levels.

They are avoided by careful observation, checking the bubble before each reading, and using the arithmetic checks.