After update 7.24 wrecked my every day spot on perfect altitude measurements, I called Garmin support. She said the trick is, do a manual calibration WITHOUT the watch on your wrist. And let the watch reach the same ambient temperature as where you are taking the reading. This winter, I would turn the watch off and leave it outside for a few hours until it was cold to the touch, same as the air temperature. Then in front of my house it's exactly 114ft above sea level. Now it's perfect every day. If not, it's usually because a storm is incoming and so barometric pressure changes it a bit. But then nightly calibration takes care of that.
The key here when doing this is to NOT use DEM or GPS calibration. You must know the exact number before you type it in. There are many free ways to find this out. And when I do it, I put the watch on the ground, still not on my wrist. If you don't, then you might have it 3 or 4 feet above the ground while holding it. Leads to a very small, inacurate reading
Accurate altitude readings is one of the bigger reasons I bought the Epix. My old FR 745 was garbage.
Hope you all find this useful! Cheers!
