Well done, Morgan. And apologies, because I also tripped over the same problem (lack of compass calibration) but I'd spaced that I had -- only because I knew that compass calibration was the next thing I was planning to do. I think it's a safety interlock but one of those MS Windows "there has been an error -- see if you can guess what it is" messages....grrr. Remember Ace Hardware sells the M6 x 10 nylock nuts 50 per box for something iike $6.99. I only discard them if I can put the nut on the prop shaft using just finger pressure. With the Hitachi electric screwdriver I've found the best torque setting is 13 which is just above the point where you can grip the casing of the motor and turn the prop by hand. Thanks Andy.