= Levelling refraction
{wiki=Levelling_refraction}
Levelling refraction refers to the bending of light rays in the atmosphere that can affect the measurements taken during surveying and leveling operations. When surveyors use leveling instruments to measure differences in height between points, the ideal assumption is that light travels in a straight line. However, atmospheric conditions, such as temperature and humidity variations, can cause light to bend, leading to discrepancies in the measurements.
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