Congratulations Wilco
Having done 6 or so nav flights, I finally got around to doing my Nav exam yesterday and passed, despite doing it to the sound of automatic gunfire and various aircraft screaming overhead at Headcorn's "Combined Ops" show.
I argee with the OP that most of the book (Air Pilot's manual) is absolute tosh, seeming to go to excessive lengths to prove how clever the author is. The one-in-60 rule can be explained in a couple of sentences yet the book does a chapter of confusing rubbish on it. I'd got about a third of the way through the book in study then ground to a halt as it's so demotivating despite being reasonably proficient and genuinely interested in the material.
But having done around 10 genuine & practice plogs, knowing how to convert units & multiply/divide use the wheel, and reading the radio nav tech section (which again though completely overdoes explanation of RBI, QDM etc) was all I really needed in the end.
Airquiz.com was useful, but as always the PPL Perfector (make sure it's at least issue 2) was a highly accurate practice for the real exam if you know what I'm saying

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