700i displaying incorrect altitude by over 250m

[SunnyAndShare]

Topographic maps of my area show the terrain at my house to be 50-55m above sea level. My GPSMAP 67 is currently showing 55m. But my Montana 700i is showing an altitude of 326m. WTF? All last week, it was showing an altitude of 410-440m, so it is getting better, but an error of 275m is not acceptable. Horizontally, the error is within reason.

I don't use my Montana much from November to April but I did install firmware 23.30 in April. I don't know if that is a factor as I did not notice this error until last week. Garmin Express says everything is up-to-date.

[GPSrChive]

But my Montana 700i is showing an altitude of 326m.

Unless you are currently in the air, this is Elevation, not Altitude.

What option do you have selected in Setup > Altimeter ?

Sounds like you may have it set to 'Continuous', which is good, as it appears to be in the process of self correcting.

I don't use my Montana much from November to April but I did install firmware 23.30 in April.

Perhaps the last time the Montana was powered on the elevation was far greater?

Leave it powered on outside for awhile so it is reading true atmospheric pressure.

See GPSrChive > Montana 7x0 > Main Menu > Altimeter for more information.

[Przekątny]

But my Montana 700i is showing an altitude of 326m. WTF? All last week, it was showing an altitude of 410-440m, so it is getting better, but an error of 275m is not acceptable. Horizontally, the error is within reason.

Incorrect elevation readings, especially with such large differences from the actual elevation above sea level, are caused by incorrect calibration.

Automatic calibration occurs after turning on activity recording based on GPS data.

Another cause may be an undeleted current activity record from the previous session (with incorrect calibration).

On the Trip Computer screen, select Reset and delete the current track, set the display of the elevation and GPS elevation data fields, also turn off Auto Start (automatic activation of activity recording), restart the device, wait until the device gains full access to satellites and then turn on activity recording.

The elevation field should display a value very close to the value displayed in the GPS elevation field.