SamT - before you spout off - go and see how much a magnetic relay affects a compass and what distance you have to move the helmet to. I agree you should never have anything ferrous near a compass and there are alternative lighting methods for compasses. The question was about the Nova. It deflects a compass a hell of a lot more than other helmet lights that I have used. I have looked at the deflection with the helmets and lights that I wear whilst surveying and at the deflection from a Nova. Mine are negligible - the Nova will cause up to 180 degrees deflection. Before you start ranting take a deep breath and chill out.