What practice involves measuring horizontal angles from backsight to foresight and checking if the sum is approximately 360°?

The practice of measuring horizontal angles from backsight to foresight and checking if the sum is approximately 360° is known as closing the horizon. When surveyors measure angles in a closed loop, the expectation is that the total of all measured angles should approximate 360°. This process is crucial for ensuring the accuracy and consistency of the measurements. If the sum deviates significantly from 360°, it indicates potential errors in the angle measurements or instrument setup that need to be addressed.

Closing the horizon helps to verify the integrity of the angle measurements in triangulation or traverse surveys. This ensures that the surveying data collected is reliable and can be used for further computations or project designs.

The other practices, such as adjusting the instrument, setting the baseline, and verifying the axes, relate to different aspects of surveying. They do not specifically pertain to the summation of angles around a point, which is the core action described in the question.