If you are zoomed in for narrow channels, it is good to occasionally zoom out to check for traffic heading your way.
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.
000 on the bearing scale refers to your ship's bow and the Heading Marker is pointing up on the radar screen so it is in the Head Up mode.
No matter what compass course your are steering, the heading marker will stay on 000 in the Head Up mode.