Before takeoff I get good a good altitude reading but once I go up for a flight and land my altimeter reads around -10 while landing. However this is an improvement over the previous -20 upon landing. Is there anything I can do to improve my reading?

r u landing on same take off spot

calibrate IMU

Having a similar problem with my Phantom 2 Vision Plus. on the ground it shows negative altitude Normally out by about 1-2 metre. Had it suddenly drop from the sky the other day after stable hover. So I have checked it over and done IMU calibration a couple of times, but still not fixed the negative altitude on the ground.

Is there anything else I can do to correct it or check the system out. Nothing obvious in the software!!

I fly  a p3p and a Rans s6 aircraft. Seeing 30 ft difference on my electronic altimeter is normal. Especially after a 10 minute warm up. Why is it important ? At 10 feet you can see it.
RayH

Is your VPS on?