The outer scale represents relative bearing. The reason why 180° is at the top is due to how bearing relates to own and target courses on the disc (for most problems, you place own course opposite the white triangle at the 180 mark at top). Please see the video link below where I demonstrate the use of the various pointers using the Sub Buddy app which is faithful to the historical disc. That example is about as complicated as the disc gets and beyond the scope of the game unless you want to simulate a no-TDC shot, but it shows all of the concepts of relative bearing, AOB, lead angle, etc. Hopefully seeing the pointers used correctly will clarify the relationships.
https://drive.google.com/file/d/1sjD...w?usp=drivesdk