​

​

​

Trained​

Expert​

Master​

Legendary​

​

​

DC​

15​

20​

30​

40​

​

​

Healing​

10​

20​

30​

40​

Level​

Bonus​

​

​

​

​

​

1​

7​

Trained​

6,5​

8​

1,5​

2​

3​

11​

Expert​

8,5​

12​

3​

2​

5​

14​

Expert​

10​

15​

7,5​

2​

7​

18​

Master​

10​

19​

13,5​

2​

9​

20​

Master​

10​

20​

16,5​

2​

11​

23​

Master​

10​

20​

21​

8​

13​

25​

Master​

10​

20​

24​

12​

15​

30​

Legendary​

10​

20​

30​

22​

17​

34​

Legendary​

10​

20​

30​

30​

19​

36​

Legendary​

10​

20​

30​

34​

If I copy the formula from the level 1 Trained cell that yields 6,5 it is "=L$8*(21+MIN(MAX(-20; $J10-L$7); -1))/20".

Translated from goobledygook into somewhat easier to understand English, the formula reads
1. Take the average healing from the optimal use case (in my example, at level 1 we shoot for DC 15 for 2d8 healing = 10 if we round it to a nice number, which we did, didn't we, my precious)
2. Find out the number of 5% units between my bonus (+7 in my example) and my target (DC 15). That number is 8.
3. Subtract the number of units from twenty (plus one, because, well, math) to find out the number of die outcomes that gives success (21-8=13)
3a. The MIN and MAX business is just there to stop the computer from going stupid, like thinking it can milk more than 10 points out of a DC 15 check by having a +15 or higher bonus.
Actually, the critical success rule allows for an additional 9 points of healing, so maybe it's smarter than I give it credit for. Anyway, these nine points are still always smaller than the +10 we get from jumping to the next higher difficulty class, so let's ignore step 3a :)
4. Each die outcome that leads to success means 5%, so sum them up to find the percentage of success (13 x 5 = 65%)
5. Multiply the healing number from Step 1 by the probability of getting it in Step 4: 65% out of 10 is 6,5.

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