Ah, the old CRP-5. Completely invalueable for the Gen Nav ATPL exam, completely useless afterwards. It's an archaic throwback to the olden days when pilots where called aviators, had fantastic moustaches, smoked pipes and referred to their aircraft as crates.
draw a line on your chart, work out your max drift, then apply the clock code to work out how much drift you need to offset. work out your groundspeed and bingo, flight planning complete. no faffing about with some overpriced piece of plastic. and as for electronic calculators, they are even worse. anything that has an instruction manual greater than 4 pages is not going to make your life any easier.