# why does elo rating uses 400 and 10?

I know how to calculate elo rating (in chess) and etc but why when it was made the inventor of elo rating decided to use constant $400$ and $10$ in expected score formula? The formula: $$ExpectedScoreA=\frac{1}{1+10^{(RactingB-RatingA)/400}}$$

• I suppose the values the function more flat, for the spectrum of elos. – ty. Jul 10 '18 at 15:47

I would assume the $10$ is just because we like computing powers of $10$. Then Wikipedia claims:
And indeed, $\frac{1}{1+10^{-1/2}}\approx 0.7597$.
(If we'd started with a base of $e$ instead of $10$, the scale factor would probably have ended up as $200$ or $225$.)