Which of the following is NOT a source of error in levelling surveys?

Explanation:

Magnetic declination is not a source of error in levelling surveys.

Magnetic Declination

• Magnetic declination is the angle between true north (geographic north) and magnetic north (the direction a magnetic compass points).
• It is primarily a concern in compass-based measurements and orientation but is generally not a significant source of error in levelling surveys, which rely on measuring height differences (elevations) between points on the Earth's surface.
• Magnetic declination does not directly affect the vertical measurements made in levelling surveys.

Additional InformationAtmospheric Refraction

• Atmospheric refraction occurs when light or optical signals bend as they pass through different layers of the Earth's atmosphere.
• This bending can affect the apparent position of distant objects and introduce errors in levelling surveys when measuring angles or distances to those objects.

Instrument Errors

• Instrument errors, such as misalignment, leveling bubble errors, and calibration inaccuracies, can introduce errors in levelling surveys.
• These errors can affect the precision and accuracy of the measurements taken with leveling instruments.

Temperature Variations

• Temperature variations can cause expansion or contraction of surveying equipment, including the leveling staff, which can affect measurements.
• Additionally, temperature gradients in the atmosphere can lead to changes in atmospheric pressure and, consequently, errors in leveling measurements.