Slide rule
I didn't think you could take an electronic calculator in with you ? I thought it was all slide rule. It would make sense if you could take a calculator, because the slide rule doesn't have the resolution required to do some of the long division required (awaiting correction from some old timer) and so has to be done by hand (a nostalgic trip down memory lane to the long division of school days).
I used my slide rule for the first year after qualifying, then moved to a flight calculator on iPhone and now have moved onto computer software.
My own personal advice, which is no more than opinion, is that I'd rather be able to go in doing the exam purely with a slide rule, just in case you find the calculator is taken off you before you attempt the exam.
Certainly if you were allowed a calculator it would explain why I finished my nav exam with like 2 mins remaining, where as all the other exams I had around half the exam time remaining when finished.