How do I create an Elo rating system?

Note: This was a question asked on Quora, and here is my answer. Click on the title to go the original Quora answer I wrote.

This graph shows Firouzja rated about 2750 is playing at 2800 level. He shortly got to 2800 with Elo.

Well, you can’t create the Elo rating system. That was already done by Arpad Elo in 1960, which the USCF adopted. Fide adopted it in 1970. Many other organizations use the Elo rating system. I have a friend on facebook, who is a mathematician, that uses it to improve his Fantasy Football results.

Elo is a pretty good rating system, but it is quite slow in its workings. This slowness has been observed by the chess world. How many times have we seen aspirants of the 2700 club play in high level tournaments and not be rewarded by the Elo rating system? “Their rating has not caught up with them yet” is what we usually hear.

In addition, the Elo rating system has a strange phenomenon of lowering the rating of a tournament favorite when that favorite wins the event. Bobby Fischer was the first player to do this when he famously lost rating points after defeating Boris Spassky in the World Chess Championship of 1972. Magnus Carlsen lost rating points when he won the Candidates Tournament prior to winning his World Championship title against Vishy Anand. There have been quite a few other times this has happened. Very recently, both Wesley So and Fabiano Caruana lost rating points for winning the US Championship…