Explanation of the accuracy score

[SandroMartens]

I am looking at these two posts and have some questions: #11148, https://lichess.org/page/accuracy.
Okay the Win Probability is some kind of logistic regression (as far as I can tell). But where does the formula for the accuracy come from? How are the parameters calculated?

[dignissimus]

I had a go at reproducing the winning chances model myself https://github.com/dignissimus/lichess-unpackaged/tree/main/winning-chances
I think the accuracy function is arbitrary. It looks like a smooth fit between some predetermined accuracy percentages for specific changes in the evaluation.

[jazzzooo]

Thank you for your research! Could you share the constants and fit of your model?

[dignissimus]

f(x) = 1 / (1 + e^(-0.0019571527373045683 - 0.0016876939916983247 * x) @jazzzooo