For the 1, two things are to be taken into account : the drill's mining speed, and the hardness of the ressource.
Stone is not the same as iron and copper. Source here : https://wiki.factorio.com/Mining#Mining_Speed_Formula
tbh, I find all this unnecessarily complicated :).

Nice, thanks for the ...

My first question is, according to the electric mining drill wiki and 0.16.51 vanilla Factorio in-game info, mining speed is 0.5, which I assume is 0.5 iron/copper/coal/stone per second. However the wiki also states that it "Mines copper, iron and coal at a rate of 0.525/s and stone at a rate of 0 ...