Hi, we live in a very rural area, however in the field next to us we have a/ Low tension ,3 phase, overhead cabling for domestic and agricultural use. b/ approximately 400m away a pylon and associated cabling for National grid High Tension, 30,000v + I have been told? On reading the full manual is mentions not being "too close" to any power cables , high voltage, pylons or any electromagnetic effect, pretty certain the "domestic" LT cables will be safe 50m away, but what about the HT? Is 400m too close to calibrate compass ?