What is the term used for the center of the protractor circle in navigation?

The term used for the center of the protractor circle in navigation is the index mark. The index mark serves as the reference point from which angles are measured in navigation and mapping. When using a protractor or similar navigational tool, this mark allows navigators to establish a baseline for determining directions and plotting courses accurately. It is essential for ensuring that measurements are taken from the correct focal point, facilitating precise navigation and positioning in various contexts, such as land surveying, military operations, or recreational activities like sailing.

Understanding the role of the index mark highlights the importance of accuracy in navigation tasks and provides navigators with a reliable point to align their instruments and readings effectively.