Hi All. New Q500 4K owner here (actually new drone user!). Bought the unit used with only 3 previous flights. Took it out for a spin this morning and noticed the altitude readout was incorrect. It was showing about -45ft when on the ground. This number continually decreased, down to -65ft the last time I looked at the reading, following a subsequent landing. I performed a compass and accelerometer calibration this afternoon. Then powered up, left the quad sitting on level ground in my back yard. It started at 0.4ft, then continued working its way down over the next few seconds. I turned it off when it got to -4ft after a couple of minutes. I would imagine this is an accelerometer issue. Is that correct? Or could it be an incorrectly aligned compass? Aside from not being able to trust the altitude readout, are there any other potential problems this would cause? I noticed it was very slow to descend for landing. Is that because it thinks it is below level ground? What would happen on RTH? Thanks for your help folks!