The most important reason for having the CRP-5 is that the CRP-1 doesn't have a compressibility scale on it, and you need it - or you did for the old CAA exams anyway, and I doubt that's changed. Also, your answers will come out DIFFERENT on the CRP-1, and different enough to give you the wrong answer in the exam! I have a CRP-5 for sale - £50 if you want it; e-mail me, though I'm going to be away for a week and won't be able to pick up e-mails till next weekend.