What is the purpose of balancing back-sights and fore-sights in leveling?

Balancing back-sights and fore-sights in leveling primarily serves to correct for instrument mis-adjustment. This practice is crucial because any tilt or misalignment in a leveling instrument can lead to errors in the measurement of heights between points. By taking equal lengths of back-sights (measurements taken behind the leveling instrument) and fore-sights (measurements taken forward), the surveyor can average out systematic errors that result from instrument imperfections. This technique helps ensure the accuracy of the readings and provides a more reliable determination of elevation differences.

For example, if the instrument’s line of sight is not perfectly horizontal due to misalignment, balancing the distances allows any potential biases in the measurement to counterbalance each other. This method effectively helps to mitigate errors, leading to more precise results in leveling operations. The focus on instrument adjustment is essential for any survey project, as accuracy in elevation determination is a fundamental aspect of surveying.