Yes @luisfsk the calculations I provide are precise. However, there is a bit more involved to understand damage prevented. I will take you a little further down the rabbit hole below.
First, being hit by an attack occurs in a few steps;
Collision - determines if the attack hits you
Elemental Effects - applies elemental effects
Mitigation - lowers damage taken
Damage Dealt - determines final damage, which includes determining if the attack has crit or not.
Mitigation is the step we are discussing. Everything I am providing in the calculations goes into damage mitigation. However, you also need to have an understanding about damage dealt by opponent.
Damage Dealt: The damage is calculated on the basis of the mitigated damage;
--> This means that Critical strikes, Exposed, ruptured... [Damage Amplifications] are applied after mitigation (thus lowering displayed damage reduction). This does not include PTL, barbarian, glass cannon Etc. Your damage prevention will also be distorted if you are not using full perseverance and if you are hit by DoT.
In our example from above, let's maintain the 61% damage reduction example. Now, let's pretend we have a match with an opponent and they land 10 strikes on you during the match. This opponent only has base critical damage or 50% more damage on critical strikes. The example I am providing will only describe one example for illustration.
Your Displayed Damage Prevented at the end of a match: 48.9k
Opponents 10 Strikes
1. Skill X 4680
2. Skill Y 1950
3. Ski!l Z 1638
4. Skill X 7020 (critical strike)
5. Skill Y 2925
6. Skill Z 2457
7. Skill Y 1950
8. Skill X 4680
9. Skill Z 1638
10. Skill X 4680
Opponent damage = 33,618
Total damage = 82,518 -->
Prevented damage = 59.27% --> (48.9K prevented /82.5K total dmg).
Blocked and Dodge attacks do not go into damage prevented display.
I hope this provides a little more clarity. My friend @Midlumer and I carefully studied this many months ago.