This presentation discusses errors in levelling and their preventive measures. There are three main types of errors: instrumental errors caused by imperfect equipment; natural errors from factors like curvature of the earth and atmospheric refraction; and personal errors from mistakes during manipulation, reading, or recording. To reduce errors, levels must be carefully tested and adjusted before use. Back sights and foresights should be equal, and field checks should be performed. Precautions like using an umbrella and avoiding noon hours can also help minimize natural errors.

1. WELCOME
A presentation on:
ERROR IN LEVELLING WITH ITS PREVENTIVE MEASURES
Presented By: Presented To:
Ashim Sharma
GE(22)
Basu Dev Bhandhari
(Department of Civil and
Geomatics Engineering)

2. Error In Levelling:
1. Instrumental Errors
2. Natural Errors
3. Personal Errors
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3. 1. Instrumental errors:
 Error due to imperfect adjustment of level
- line of sight not perfectly horizontal(leads to collimation error)
 Error due to sluggish bubble
- remains central though the bubble axis not horizontal
 Rod not of standard length
- incorrect graduations of the staff
 Error due defective tripod
- instability of instrument due to shaky tripod
 Zero Error
- if the zero point of the graduation of staff is not exactly at the base of the
staff
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Fig:- Collimation Error

5. 2. Natural Errors:
 Earth’s curvature
- line of sight deviate from a horizontal line, lowers the elevation
 Atmospheric Refraction
- the line of sight is refracted towards the surface of earth in a curved path, raises
the elevation
 Variations in temperature
- expansion of the bubble due to temperature, shifting of bubble to heated end
 Wind vibrations
- high wind shakes the instrument and disturbs the bubble and the rod
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Fig:- Error due to curvature Fig:- Error due to refraction

7. 3. Personal errors:
 Mistakes in manipulation
- error in setting up the level, parallax, staff not vertical
 Mistake in reading the rod
- Reading against top or bottom hair instead of central hair
 Errors in sighting
- difficult to see the exact coincidence of the cross hairs and staff graduation
 Mistakes in recording and computing
- digits interchanged, entering B.S & F.S in wrong column, arithmetical
mistakes
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8. Error Adjustment:
We can also adjust the error by following ways:
1st method: If the distances between points are known then the correction will
be distributed over the distances.
Correction Formula: (total error*distance)/total distance
2nd method: If the distances are not known then the correction can be
distributed according to the number of instrument positions.
Correction Formula: (total error* no of instrument setup)/total no of
instrument setup
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9. Preventive Measures
Here are some methods for reducing the errors in levelling:
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• Level must always be carefully tested and adjusted before used.
• Back sights and Foresights should be made equal.
• Observing the bubble after target has been sighted.
• Rod graduation should be tested and compared with any standard
tape.
• Every screws and bolts of tripod should be checked
• For removing zero errors, levelling is started and end up by the
same staff.

10. Preventive Measures
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• Staff readings should be kept small neglecting the surface of the
earth.
• Use of umbrella to protect level and instrument.
• Avoid levelling during noon hours.
• Hold rod firmly; Use head/body to support it.
• Usual field check should be done.

11. References:
 Agor, R. (2012). Surveying and Levelling. Khanna Publishers.
 Punmia, Dr. B.C. (2005). Surveying Vol. I. Laxmi Publications.
 URL 1: http://aboutcivil.org/errors-in-levelling.html| Accessed on:
21Jan,2017
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