In scrabble, how does the Elo rating system work?

I’m not absolutely sure about the exact formulas; it’s a bit complex, but the gist of it is: You start with a set rating. When I began playing tournaments, the start rating was 1200. In case you win a game, your rating rises. The better your opponent, the more rating points you earn.
On the contrary, your rating goes down if you lose a game. The weaker your opponent, the more rating points you lose. The span between your potential rating gain and loss is always 20 points. Thus, for instance, playing a far higher-rated opponent might suggest that you will get a +16 if you win and a -4 if you lose. If you play a lower-rated competitor, it would be the reverse.