I've read the many posts discussing the need to remove one's watch, keys and phone before a compass calibration, and it makes perfect sense. If you had to guess, how large is the radius around the unit to keep metal-free? If there are things like power lines or chain-link fences within 10-12 feet of the unit, is that too close? Or is this just a problem for metal within, say, 2-3 feet?

I live in a somewhat dense city, and would like to know if I need to leave my small backyard to get a proper calibration.

Thanks everybody!

Hi, it's better to go far away from the power lines or chain-link fences.
There's not an accurate distance, we'd suggest you to do the compass calibration in an open area.