In the Polkadot wiki I see that "validators are paid proportionally to the amount of era points they have collected" after every era. However there is no info about how many DOTs an era point is or what is the exact proportional relationship between the two.
Moreover, digging into polkadot.js staking interface, one can see that these two variables are directly proportional (see image below). But if we go to the detail, we see that the coefficient of proportionality is not constant between eras and there is a small variance. How is this coefficient calculated? Is there an explicit formula linking era points and rewards in DOTs per validator?