Board Game Arena

I have played over 200 games and can see no logic to the way elo is calculated. Is there an explanation somewhere? I read about the K factor and the other obvious but no explanation on how they actually calculate the change in elo after a game.

It works the same in all games (except cooperative and solo-only): https://en.wikipedia.org/wiki/Elo_rating_system

For example, take https://boardgamearena.com/table?table=892563626
You can see the numbers by hovering on the elo scores

Before the game:
Player A: 283.35
Player B: 177.93

Result: Player A won

Rating exchanged:
K = 20 (assuming both players have played more than a few games already)
D = 177.93 - 283.35 = -105.42
K * (1 - 1/(1 + 10^(D/400)) ) = 7.06

BGA-specific clutch:
3 consecutive wins, exchange reduced to 97%
7.06 * 0.97 = 6.84

After the game:
Player A: 283.35+6.84= 290.19
Player B: 177.93-6.84 = 171.09

This doesn't exactly match the BGA display, probably because the 97% is not accurate, or because rounding is applied at different steps. It looks like the reduction is actually x^2/36, that gives 2.78% instead of 3%, with which (i.e. 97.22%) the exchange becomes 6.86 instead of 6.84, exactly matching the display.