What is one of the functions of the cover on a lensatic compass?

The cover on a lensatic compass serves the essential function of containing the sighting wire, which is vital for accurate aiming. When using the compass for navigation, the sighting wire allows the user to align the compass with a specific point of reference in the distance. This ensures that the user can take precise bearings by looking through the cover at the target while aligning the compass with the earth's magnetic field. This function is crucial for accurate navigation and effective use of the compass in tactical situations.