Garmin Edge 500 and Garmin Edge 800

We went riding today. Only 2.25 miles but it was nice.
I have a Garmin Edge 500 on my road bike
My SO has a Garmin Edge 800 on his bike.
Mine shows an elevation of 131, his 89 ft. I've read that the elevation gained number on the units might not be right, but wow, that much of difference, what gives.
His mileage is 2.24; my mileage is 2.19. I know that isn't much, but why the difference?
The average speed and highest MPH are different but I expected that as we both ride differently even on the same trail.

In my experience, satellite GPS are just more variable than other ways of calculating distance. I've heard people theorize that if it takes readings when you've just gone around a curve, it will plot the distance as if you had been going in a straight line... and perhaps even if it's just a few seconds between readings (I have no idea) that would end up being significant. I do know my Garmin 500 always read a bit "short." (And I wish I could find it! I don't want an 800... the 500 was awesome with maps and everything I needed...)

Five hundredths of a mile ... there could have been that much REAL difference in the distance two people rode on two separate bikes. You know when you run a race, and your watch always shows greater than the certified distance of the course? That's partly because of imprecision in the watches, but much more it's because you'd have to perfectly run the shortest set of tangents to get the exact distance.

As far as elevation, even with a barometric altimeter there's plenty of inaccuracy just because of atmospheric conditions.

Are they both set for "smart" recording, or one second recording (as Geonz suggested)? Do you have wheel sensors on both of them? Wheel sensors will make your speed and distance data a lot more accurate.

Also, did you let the barometric altimeters "settle" before you turned the timers on and started riding? It takes about 20 minutes for my 705 to stabilize after I turn it on. I expect the newer units aren't any different in that department.

And finally ... are those the raw numbers in your computers? How did they compare once you'd downloaded it to your various software? Which apps or sites do you use? I don't know enough to say which has better correction on which parameters than others, but they all have some data correction, and it does seem to me that these days, the ones that rely on Google maps are more accurate than the ones that license Navteq.

Thanks for all the information. I am going to look into your suggestions. It's not that important an issue, I was just curious why it happened.