elan,
I'm not sure what you are saying makes sense, or I'm mis-understanding you.
Examine the pic of the SHIV TDC. You are saying that the relative bearing is read from the inner dial, but from what index? As far as I can tell, the inner ring of the lower dial is a fixed compass rose around your ship, and the "arm" moving across your bow is the gyro angle of the solution as read against that inner ring. In your example, the relative bearing is reading zero, but It will *always* read zero....
Edit: Ahh, it seems that the outer ring of the bottom dial represents true heading of own ship. It's basically a compass when read against the inner ring "ownship" image. So, that sums up the bottom dial... ownship heading on outer ring, gyro angle on arm.
That leaves the top dial yet to be understood by my challenged brain hehe.
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