If it’s a GPS issue, the track would show it.
The 745 has a barometer and you can switch it between measuring altitude and pressure (for weather without climbing).
It’s possible that the GPS was off and it was using the wrong location to “calibrate” the barometer at first. Then when the GPS kicked-in with the right location, the baseline for the barometer changed.
As far as I know, this “calibration” requires explicitly saving points and indicating the known elevation (it’s a deliberate process that people would likely remember doing). Most people don’t do this (it’s extra work). It also doesn’t effect gain numbers anyway. Which is what most people are interested in (people don’t usually care about absolute altitude).
Again, the track would show issues with GPS.
The barometers can take some time to adjust to ambient pressure but that wouldn’t cause an abrupt change.
Last edited by njkayaker; 01-23-23 at 07:44 AM.