Originally Posted by
terrymorse
GPS is terribly inaccurate at measuring elevation. If you are using a phone to record a ride, that easily explains the wide variation in elevation gain.
Barometric pressure is much more accurate. But errors can creep in there, also. If the pressure rises or falls during a ride, the device will record it as phantom elevation loss or gain.
There’s “yabut” in there. GPS is slower in measuring elevation so it varies more when moving. Barometric pressure altitude measurements are quicker but they are influenced by more factors…temperature and pressure, as you pointed out…which can lead to errors. Both have about the same amount of error in measurement. If the phone is depending on the GPS signal for altitude, the errors might propagate faster because of the slow measurement