I work in the land survey industry. One of the tools we use on a daily basis to locate survey monuments is a magnetic location device. This tool is highly sensitive to a magnetic charge and, through visual and auditory means, tells you how close you are to charged objects (usually metallic). One thing we know, is that while using this device, it is extremely hard to get good readings while there is as cell phone in your pocket or in your general vicinity. They throw a very strong magnetic field that makes our locator scream (literally... thats the best description of the sound). With this in mind, I usually keep my Tx and phone about 10' or more away from the Vision during calibration and take-off. I am 1000% sure my cell phone can cause calibration/compass issues so I keep it at distance when I can. Just food for thought (maybe this has already been discussed).