What must be used to obtain target ranges in radar navigation?

In radar navigation, range markers are essential tools for obtaining target ranges. They serve as visual aids on the radar display that help mariners ascertain the distance from their vessel to the targets being monitored. Range markers can be adjusted on the radar screen to indicate specific distances, allowing operators to measure how far objects are relative to their position in real time. This is crucial for navigating safely and avoiding collisions, as it provides valuable information regarding the proximity of other vessels, landmasses, or hazards.

Fixed markers and distance units may provide some context, but they do not serve the same operational function as range markers in the dynamic environment of radar navigation. Speed measurements are relevant for determining how quickly a vessel is approaching or receding from a target, but do not directly indicate distance. Therefore, range markers are fundamental for accurately gauging distances on a radar display.