I fly Cessna 172 and Cherokee Warrior both older models without a GPS. I have a very useful freeware navigation app on my android phone which is really good in every regard other than it always reads my altitude a bit higher than were I am.
Best example is when I am taxiing my track and its projection on the ground which should have merged are separate.
The app does not have any setting for adjusting this! I wonder if there is any explanation for this. The app superimposes my 3d coordinates on a moving sectional chart. I re-installed the app which didn't help.
Here is my flight KML on Google Earth on my approach and landing to Catalina airport last Sunday.