I don't have SH5, but since SH1 through SH3 had something similar I suspect the sonar display works the same. This is from SH4;
Top is always 0, since the ship's head is zero and all relative bearings are a 360 degree compass from that reference point. The inner ring is a gyro compass repeater to show true bearings. Looking under the zero in the outer ring I see 335, that's the sub's true heading. Lookout reports sighting bearing 090, look at 090 on the outer ring, lined up with that on the inner ring is 065 true. No math.
