Sometimes all you have to do is move the craft to another location 30' away and it will come in range 1400 to 1600, such as moving off of concrete with rebar beneath. Sometimes all you have to do is move yourself away from the craft. But if those don't work you should re-calibrate in an open field. I personally don't like calibrating in new areas because you never know what's below you or around you that may cause a magnetic anomaly. If there's a magnetic anomaly where you're calibrating and you perform a successful calibration, you may have just acquired a really good BAD calibration, and don't know it. I like calibrating in places that I've calibrated before successfully and has worked for month with no problems. But, if you're out and about an need to calibrate, get out in a field somewhere as best possible. Never do it over concrete, which can have rebar in it. Try to avoid asphalt, but I've done it many times without an issue, just hold the bird way up over your head as high as possible, that's what I do. Some folks say the asphalt can be a problem for some reason, not sure why.
Always look at the mod value after a calibration when you're 100' up to make sure things look right.