>>2154309
The formula in that picture is wrong, I don't know if that's an old version of the help menu or what, but this is the AT code from the game (addtime is cast delay).
Essentially the way to think about it is like this:
>base AT is 18
>at 100 speed you add 36 to it (for 54 AT turns) which you can think of as the baseline for your headmaffs
>at 200 speed you add 18 to it (for 36 AT turns), double speed = half number added
>at 50 speed you add 72 to it (for 90 AT turns), half speed = double number added
No matter what there's a lower limit of 36AT from speed and cast delay (if there was a negative cast delay), but masteries that trigger at turn end like Best Condition can get around that. There's also an upper limit of 360 during your turn, which you can see if you Strong Slowdown white clown masks