I came here after four years break. No matter for reasons, but I decided to participate to see how I can perform today. You know, years go by, covid eats our brains etc. From rating 1741 in 2018 now I dropped to 1597, performing on level of 1100. This was sad to me, but I was prepared too see I declined. However I was surprised how much I dropped. Started investigating a bit.

First I was trying to look at other players. I found one that is really interesting. Actually he's a hero for me, because Codeforces Round #777 (Div. 2) is his 777-th round! Best regards ruban :) If you take a look at his rating chart you'll notice a drop in rating somewhere in 2020. At first sight seems to be a 150 points drop.

There are some mysteries behind Elo rating system. I am not an expert, maybe some of you know it better. But there are ideas that huge growth in players caused by covid may cause rating deflation, like this discussion on a chess forum. At Codeforces we also experienced huge income of players in 2019 and 2020. Just taking random contests from 2019 and 2021:

• Codeforces Round 538 (Div. 2) 2019-02, 6141 players solved A
• Codeforces Round 700 (Div. 2) 2021-02, 13356 players solved A

(By the way, such growth is not visible in problem C.)

It's important that I look at cyan segment. Things may look differently in other segments, especially in red group.

So I am writing this to share my thoughts and possibly make us all conscious of the fact. But also to ask:

Can you say more about rating deflation on Codeforces? Is it possible to calculate what number today resembles given number in 2018? Of course I'm interested in a number that reflects actual skills, although I know Elo is in general relative.