So I've ran into this problem with my Mavic 2 Zoom. This started sometime back when I came back to my takeoff point/area my altitude actually shows a negative altitude rather than actual. For example if I take off and my altimeter is showing 4ft and then I go and fly around and come back to that same point rather than it reading that same 4ft in altitude is showing -5ft for example, like somehow my drone is flying below me if that makes sense. It's like I've gone below my actual height and will be anywhere up to 20ft off from its actual altitude. I've calibrated everything and anything I can and it's continues to do it. Has anyone encountered this issue? I can gauge 5ft easily but my controller is showing my drone at a negative altitude which is virtually impossible, and I can understand if I was landing at a different spot that was considered lower than my takeoff point but when I'm going to the exact same spot there's just no way for it to be off so much.

Altitude in DJI aircraft is measured by a barometric sensor, exactly the same technology used in full-size aircraft. None of the user calibrations do anything to the barometer, so re-calibrating is just wasting your time. The barometer is set to zero when you take off, and because barometric pressure is not constant over time, it is possible that over the duration of your flight, the pressure has changed slightly. This is why when you return, the displayed altitude may have changed.

Geebax Posted at 1-2 21:47
Altitude in DJI aircraft is measured by a barometric sensor, exactly the same technology used in full-size aircraft. None of the user calibrations do anything to the barometer, so re-calibrating is just wasting your time. The barometer is set to zero when you take off, and because barometric pressure is not constant over time, it is possible that over the duration of your flight, the pressure has changed slightly. This is why when you return, the displayed altitude may have changed.

But the problem is it never did that the first 6 months of usage, it’s never been mishandled and after a years usage still haven’t reached 100 flights. I can fly my mavic mini from the same takeoff point and run the exact same route and it show the correct altitude and not have a +/- of 20ft or more, thats just terrible. I could understand a few feet but when is that’s drastic something is wrong. Hell I can takeoff and go to default altitude of 3/4ft let it hover and with a short time my altitude will already start going off. I don’t know if sending it for repair to DJI since it hasn’t been a full calendar year since my purchase just yet but coming up close, I just don’t want a refurbished aircraft.

GWURT Posted at 1-3 18:15
But the problem is it never did that the first 6 months of usage, it’s never been mishandled and after a years usage still haven’t reached 100 flights. I can fly my mavic mini from the same takeoff point and run the exact same route and it show the correct altitude and not have a +/- of 20ft or more, thats just terrible. I could understand a few feet but when is that’s drastic something is wrong. Hell I can takeoff and go to default altitude of 3/4ft let it hover and with a short time my altitude will already start going off. I don’t know if sending it for repair to DJI since it hasn’t been a full calendar year since my purchase just yet but coming up close, I just don’t want a refurbished aircraft.

But the problem is it never did that the first 6 months of usage.
Possible but unlikely (unless you flew very little) as air pressure is always changing, it just doesn't change much over the duration of a drone flight.
But +/-10 ft changes are common and normal, sometimes up to 20 ft.
The explanation above is accurate.

Labroides Posted at 1-3 20:28
But the problem is it never did that the first 6 months of usage.
Possible but unlikely (unless you flew very little) as air pressure is always changing, it just doesn't change much over the duration of a drone flight.
But +/-10 ft changes are common and normal, sometimes up to 20 ft.

Okay, so if its typical then I can and will be more understanding. Im just agitated watching my drone bob up and down rather than remaining at its constant altitude, but if barometric pressure is what causing that then my triple the cost Mavic zoom is garbage over my Mavic Mini which stays constant and doesn't look like its dancing around while flying next to each other with my kids on a regular basis, so much so that even they ask why my Zoom doesn't remain still. this is every flight and only started some months back. Im not an expert but im observant enough to know how things started and where they are now. I'll use the insight and learn from it

GWURT Posted at 1-3 21:39
Okay, so if its typical then I can and will be more understanding. Im just agitated watching my drone bob up and down rather than remaining at its constant altitude, but if barometric pressure is what causing that then my triple the cost Mavic zoom is garbage over my Mavic Mini which stays constant and doesn't look like its dancing around while flying next to each other with my kids on a regular basis, so much so that even they ask why my Zoom doesn't remain still. this is every flight and only started some months back. Im not an expert but im observant enough to know how things started and where they are now. I'll use the insight and learn from it

Im just agitated watching my drone bob up and down rather than remaining at its constant altitude, but if barometric pressure is what causing that ...
While slow and slight air pressure changes are responsible for indicated altitude variations between launch and landing, it has nothing to do with your drone bouncing around in the air.
If it did, you'd be seeing the indicated altitude bouncing around too, but air pressure changes very slowly.

I'm unsure what's making the M2 bounce around.
How much movement are you seeing?
The specs say:
Hovering Accuracy Range   

Vertical:
  ± 0.1 m (when vision positioning is active)
  ± 0.5 m (without vision positioning)

How does yours compare with that?

Labroides Posted at 1-4 05:38
Im just agitated watching my drone bob up and down rather than remaining at its constant altitude, but if barometric pressure is what causing that ...
While slow and slight air pressure changes are responsible for indicated altitude variations between launch and landing, it has nothing to do with your drone bouncing around in the air.
If it did, you'd be seeing the indicated altitude bouncing around too, but air pressure changes very slowly.

The altitude actually does fluctuate and that's were the problems start because of the constant fluctuations the altimeter doesn't remain accurate, so if it creeps up a few feet and then back down, and then down and back up this is a lot of times were my altitude accuracy start going off and the longer I allow it to do that the more off it goes and I always have to remain engaged on the controls. The worst I've seen my altitude accuracy off was almost 40ft, where as im actually hovering a few ft off of the ground and the drone is showing if I recall -30ft which is equivalent to like if I took of from a 3 floor parking garage a went to land it on the street level. I can't even take hyper lapse video because my drone drifts and bounces around every time I fly around so I dont even bother with it anymore.

As far as the Vertical: its varies but it definitely not mild like the specs say, its pretty drastic at times any where from +/- 3-5 m with either or setting. I've considered rolling back the firmware because it seems like that it started happening around the time the most recent version was rolled out back mid last year July if I recall. I just haven't done so because I've been searching to see if its something I was doing wrong or if indeed it is the drone. I tried local forums and they suggest changing the props so I did so and there was no change, I thought also it was the time I was flying around which is dusk to evening hours and tried mid-day but there was still no change. Im no expert by any means which is why im open to all suggestions and providing the information that I encounter and not being exaggerated at all even though it sounds that way. I alway make sure that I have a good strong satellite/GPS signal along with my checks before taking off every time just to eliminate that also.

GWURT Posted at 1-4 08:27
The altitude actually does fluctuate and that's were the problems start because of the constant fluctuations the altimeter doesn't remain accurate, so if it creeps up a few feet and then back down, and then down and back up this is a lot of times were my altitude accuracy start going off and the longer I allow it to do that the more off it goes and I always have to remain engaged on the controls. The worst I've seen my altitude accuracy off was almost 40ft, where as im actually hovering a few ft off of the ground and the drone is showing if I recall -30ft which is equivalent to like if I took of from a 3 floor parking garage a went to land it on the street level. I can't even take hyper lapse video because my drone drifts and bounces around every time I fly around so I dont even bother with it anymore.

As far as the Vertical: its varies but it definitely not mild like the specs say, its pretty drastic at times any where from +/- 3-5 m with either or setting. I've considered rolling back the firmware because it seems like that it started happening around the time the most recent version was rolled out back mid last year July if I recall. I just haven't done so because I've been searching to see if its something I was doing wrong or if indeed it is the drone. I tried local forums and they suggest changing the props so I did so and there was no change, I thought also it was the time I was flying around which is dusk to evening hours and tried mid-day but there was still no change. Im no expert by any means which is why im open to all suggestions and providing the information that I encounter and not being exaggerated at all even though it sounds that way. I alway make sure that I have a good strong satellite/GPS signal along with my checks before taking off every time just to eliminate that also.

Props and GPS won't make any difference to altitude holding.
The only thing that might make a difference would be to re-calibrate the IMU.

I wrote a script to fix the SRT file altitudes. Works for DJI FPV.

https://github.com/clay584/dji-fpv-alt-srt-fix