The RBI headache of 50+ years ago returns! I remember being taught (in the ground school at 5 FTS RAF Oakington) on the Vickers Varsity how to employ the "parallel needles" technique which involved setting the required bearing on the compass (G4B?) heading selector and turning (drag or push) until the ADF needle was parallel to the heading selector and then turning onto the heading plus or minus the drift - of which there was no indication. Sorry to ramble on about such a distant memory.