Mastery & Resistance

This experiment does not show how to calculate mastery or resistance.
Please visit a separate section for this purpose here.

I started this experiment because of my curiosity whether this picture,
which was shared by developers to community,
is just a visualization or whether the arrows really show something.
And if so, then what? 

I did choose Poison as a testing object.

Poison skill to Poison resistance it was immediately clear that there will be less damage.
But do the arrows really show anything more?
Will Electric or Fire element have higher damage to Poison Resistance?

As a testing animal I chose a Giant Salamander,
which has a maximum of 150,000 hp and poison resistance.

I took the items off so they wouldn't affect my stats, so the experiment was clean,
without my Mastery and Resistance and the distractions in the form of random skills.
My attack damage without any armor was 2014.

I had to find one salamander to test it all on.
If someone killed it, I'd have to start the experiment all over again.
I did find Giant Salamander level 77 - 124,000 hp.
I made a video so I wouldn't waste time with the counts for each attack.

If any skill did critical hit, only thing needed was to divide value by 3,
because critical hit is 3 time higher normal hit.

I apologize for the translation mistake. Diameter I mean as an Average.

How did I calculate the average?
I just divided Pure Damage with Damage to animal.
15,548 / 2,800 = 5.552857142857143 ≐ 5.55

Result

It's simple. Looking again at the illustration of the elements,
we now know that the arrow shows Mastery.

To Poison resistance is best Fire mastery
To Electric resistance is best Poison mastery
To Cold resistance is best Electric mastery
To Fire resistance is best Cold mastery

Even if you have no Mastery, the mastery element has a 15% bonus damage to the resistance element.