I can't remeber which model it is exactly.... but my casio has an excellent conversions function..... converts km to nm, inches to meters, US gal to UK gal...... about 40 conversions in all I think. Really really excellent for gen nav.
Do a search. I found the recommendation on an old post. Cost about a tenner. It really did take take some of the stress out of the time pushed gen nav exam. Oh, and it has a degrees, minutes button too.