If you are zoomed in for narrow channels, it is good to occasionally zoom out to check for approaching traffic.
Since this range scale is set at 3 miles, the distance between each ring is 1/2 mile.
If the radar is not receiving compass data, it defaults to Relative Motion Mode.
In Head Up mode the Heading Marker will always stay on 000 no matter what compass course you are steering.
Since 000 in the Head Up mode refers to your ship's bow, the radar's Relative bearings would need to be converted to True bearings before plotting on a chart.