My electronic compass has never failed me yet. But, I know they can and do get out of "calibration". Had our dive instructor go out on a night dive and it sent him off in the wrong direction. I have frequently had to calibrate the one in my Garmin Alpha 100 GPS/Tracking unit. I think it would be a good idea to carry a mechanical compass in my BCD as a spare/just in case. I would like to hear anyone's recommendation of which ones they feel are good. it should be accurate and big enough to see and easy to read. I don't need one with bells and whistles and extra stuff. t just needs to be as reliable as possible and not fail if and when I need it. Don't really care about the price as long as it's a good one and will take 130 feet of depth. Thanks in advance for any information, it is greatly appreciated.