What method is employed when the distance between two points exceeds the maximum length of sight?

Reciprocal leveling is employed when the distance between two points exceeds the maximum length of sight. This method is particularly useful in situations where direct sight between the two points is not possible due to obstacles or the curvature of the earth. In reciprocal leveling, two instruments are set up at each point, and measurements are taken from both locations to determine the height difference accurately.

This technique helps to mitigate systematic errors that may arise from atmospheric refraction or other environmental factors. By taking readings from both locations, surveyors can achieve a more reliable and accurate measurement than that which could be obtained from a single setup point. It's essential in surveying across longer distances, establishing vertical control, and ensuring precision in large-scale projects.