Baro/Alt "auto" mode needs to be better - altimeter drifts when I'm sitting around indoors

multiades said:

Just calibrated altimeter manually. 60 seconds later it's -10 ft. I'm sitting in a chair in front of the computer.

Unless you're sitting in front of a A/C or heating vent, a 10 foot change in 60 seconds sitting at a computer suggests the manual calibration was to the wrong value and the watch is correcting itself, or the port may be partially obstructed and the watch thinks the correct calibration is wrong. 

Wrong value? It shouldn't be pulling the value from anywhere else - GPS is not active so it's not trying to get GPS or DEM elevation. I'm punching in a value manually and it's drifting on its own. I don't think the GPS could even get reception where I am sitting. No air conditioner running and the temperature of the internal watch sensor should be stable for hours now.

The port is unobstructed, altimeter seems pretty responsive during activities and the barometric pressure chart always looks similar to a local weather station. I don't think the watch has anything wrong with it. The rapid 10' drift is not a frequent thing, but the watch will inevitably drift over a day of not leaving the house. If I'm not out and moving around, I think the software should be smart enough to figure out that pressure changes are entirely due to weather.

EDIT: it happened again. I set the altimeter, and it drifted down 11 feet in 2-5 minutes. I haven't moved out of my chair the entire time. That's 3 times in a row. Yes the local barometric pressure is probably rising.

And again, I set it and it's down 8' in another 2-3 minutes.

Is the barometer (in the baro widget options) watch mode set to “Altimeter” by any chance?

that makes the watch interpret any changes in ambient pressure as altitude changes, regardless if it is true or not

If you are at the same altitude for a long time and want increased barometer accuracy you can set it to barometer mode (which interprets any pressure changes as ambient pressure, not altimeter changes)

the best mode to set it to if neither of the above are desired is “Auto” mode which tries to guess if you’re going up in altitude or if weather pressure changes

altimetry is very tricky and a complex subject

multiades said:

Wrong value? It shouldn't be pulling the value from anywhere else - GPS is not active so it's not trying to get GPS or DEM elevation.

I never said anything about GPS. You said you're manually calibrating your watch.  Based on what?  A weather station? How close is that weather station?  Is it taking measurements from the same elevation as your residence? For example, if f you entered 30.10 inHg and that isn't correct, the barometer will automatically adjust. 

By the way one of the most important metrics for airplanes is altitude, and they run into the exact same issue

local pressure is influenced by both altitude and weather at the same time and there is no absolute way to distinguish between the 2 if you can’t fix one of the variables

Whilst you’d think airplanes with all their expensive equipment have a way around this, the solution is as basic as it is archaic: trade safety for accuracy (either you set your altimeter reference to the lowest area value (area QNH, or airport QNH which fixes one of the variables), or rverybody sets his reference to thr same arbitrary level so collisions are excluded and fly high enough so terrain is not an issue). 
Either way, no airplane knows it’s exact altitude at any point (unless GPS is used, but that then carries its own set of issues)

Are you calibrating just the altimeter to a known elevation and not the barometric pressure at the same time? I can manually enter an elevation and this will change my barometric reading.   Depending how quickly the barometer starts correcting itself, it may think this is due to elevation change.  Do you have this problem if both elevation and pressure are manually calibrated to the correct values at the same time? 

tess - I know what altitude I live at, so I set it to that altitude (at this rate, several times a day). Only altitude can be set, and the watch infers barometric pressure from the altitude reading (presumably it's using a standardized table, this makes perfect sense). There is no way to set pressure directly.

When I'm comparing to a local weather station, I'm just looking to see the timing of trends up and down and by how much. I'm not putting any emphasis on exact values. My watch is roughly matching the local station.

claude512 said:

By the way one of the most important metrics for airplanes is altitude, and they run into the exact same issue

local pressure is influenced by both altitude and weather at the same time and there is no absolute way to distinguish between the 2 if you can’t fix one of the variables

Whilst you’d think airplanes with all their expensive equipment have a way around this, the solution is as basic as it is archaic: trade safety for accuracy (either you set your altimeter reference to the lowest area value (area QNH, or airport QNH which fixes one of the variables), or rverybody sets his reference to thr same arbitrary level so collisions are excluded and fly high enough so terrain is not an issue). 
Either way, no airplane knows it’s exact altitude at any point (unless GPS is used, but that then carries its own set of issues)

I have done a little flying and I know about this part including setting it to 29.92 above FL180 (don't ask me how I remember that). The whole objection I'm putting forward is that the watch needs to be smarter about which variable it's fixing when in "auto" mode. In a plane in motion, you can never assume either is truly fixed. When I'm hanging around the house, elevation should never change, and the watch should be smart enough to figure out that I'm not walking around anywhere and lock my altitude as baro changes.

Maybe the watch interprets typing as going up and down stairs. I was hoping it would be smart enough to figure that part out.

And as I'm typing this, I set elevation again, and it dropped by 10 feet again. It's possible the pressure sensor has poor precision near sea level and that improves in the "middle" of the range (assuming the watch is designed to measure up to significant altitude). Regardless, from a software perspective, it should be ignoring altitude changes that occur when I'm sitting down at a computer and register a change to the barometric pressure only.

I just want to emphasize that I understand the relationship between pressure and altitude very well. I understand the watch is only reading pressure and pressure changes. I get how all of this works. If you read a little deeper (and the title of the post), I'm taking issue with the fact that the "auto" mode isn't smart enough about when to treat the barometric pressure input as an altimeter, and when to treat it as a barometer. It should be able to figure out whether I'm really moving around outside or climbing stairs versus walking around the house, or sitting at a computer. The problem occurs because it's not doing a good job of "freezing" altitude when altitude should not be changing. Fundamentally the accelerometers that record activity can't figure out if I'm typing or walking down stairs - THAT'S the problem I'm raising.