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That's quite an old article. It was replaced back in 2015 and that is still probably out of date.
out of curiosity what is the most recent one?
by the way I did not checked the math but I do trust the work done making article, still the data I see there contradict my experience, speking about my rating (somenthing around 1.800 and 1900 in daily and somenthing around 1.600 and 1.700 in 3 min blitz) and other players with a comparable strenght I find 1.700 in blitz too high on average for a 1.800 daily player, I can't figure out at all a 1.800 daily rating corresponding on the average to 1.800 fide rating. My guess it's that even if the article is old it's rithwer that the number of data was not enough to have a a more precise result or either that there was some selection bias.
Here it is I think https://www.chess.com/blog/smarterchess/chess-rating-comparison-2016 There will be some selection biased particularly for FIDE and USCF ratings because if yours is quite a bit lower than your raring on this site than you won't post it will if it's higher then you will. For instance I have a mediocre FIDE rating that I don't post.
this should give you a good idea. btw, lol at all the people giving nonsense,answers, which they believe to be funny (which, of course. they are not).
i recently played over the board and beat players higher then 1350 which is around my chess.com rating. I have played OTB before though. So it all depends on your experience and preparation.
Keep in mind psychology and nervousness plays a bigger role when playing chess in real life.