My ELO is 1000 on a good day. Magnus’ is, let’s say 2800. If by some miracle I play him to a draw, do both of our ELOs stay the same?
Assuming you’ve played 30 games, yours goes up 10 points and his falls 10 points. (If not, it would be 20 points each.)
Here’s an explanation of what the K factor is. (The actual calculator part seems broken, though.)
The Elo rating system sets a maximum difference limit of 400. FIDE Rating Calculators
So if you’re rated 1000, you get the same improvement (about 8.5 points) whether you draw with a 1400 or Magnus Carlsen.
(I once beat the German grandmaster Hubner when he was rated over 400 points more than me. Mind you he wasn’t very good at table-tennis. 
)
Sorry – ignore my post.
Thank you for that last sentence; it reminded me of this xkcd.
There is a game that does something similar:
Brian