2 resourses which were very valuable to me when I studied for the master's test were Mike Holt's Exam Preparation, which had 100's of practice questions and illustrated step by step info on working out calculations, load calcs, xformers, etc. Also Tom Henry's Exam Workbook(comes in Master's and Journeyman). Tom's book has very challenging exams using the 50 or 70 question format you most likely will get in the actual test. You need to practice doing actual number, random question tests for speed in the NEC, this is where most people get hung up. You'd be surprised how hard it can be to do these under time/pressure, but also how much you can improve with practice. I got really quick with practice, but to be honest right now I couldn't do it nearly as fast as when I was studying for the test.