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1. On the radar screen, the circles that mark fixed ranges. On the 6-mile range, for example, range rings are typically shown at 1.0 mile intervals. Some modern radars let users select the ring spacing. See also portable range scale.
2. In electronic charting navigation, range rings on marks and waypoints and vessel icons can aid our navigation in various ways. Setting six rings with 1-mile spacing on our vessel icon as it moves across the chart, along with the standard heading line, is a quick way to compare what we see on the radar with our charted position according to the GPS. This is a valuable trick to keep in mind, even when you have a radar overlay option for the chart. The latter can sometimes be very congested and hard to read.
Accurate fixes can be plotted quickly on an echart using two ranges measured to two targets with the radar. We just place a mark on each target and put a ring on it equal in length to the measured range. The intersection of the two rings is an accurate fix, independent of the vessel heading. (Other radar piloting fixes rely on an accurate heading sensor.)
It is common practice to put a range ring on a waypoint of a route being followed at a distance equal to when we want to turn to the next mark. This can trigger changing the next waypoint to be the active one or just sound at alert that you are there. These types of rings are often called arrival rings.
Or we could place a mark on a charted rock with a ring on it set to the distance we want to stay clear of it.
In qtVlm range rings are called "circles" on the set up pages.