Hi All, anyone know what if any is the purpose of the angle graduations on the cambelt cover? Thanks!

Same thing from a different angle

 

for tdc purposes i think

 

As above,timing marks for top dead centre.

 

It's for checking the running ignition timing (advance/retard) with a strobe light.

Relic from the days when cars had manually adjustable base ignition timing. Have no idea why Imprezas still had them (or other cars at that).

Here's the procedure...

http://www.sulegacy.com/ignition_tim...tion-3861.html. For a legacy, but same for Impreza, as well as pretty much every car made prior to 1990 with a distributor.