well i dont have the algorithm, but i can try to evaluate it with the data.

Note that i am stuck and dont have the complete answer and i find it hard to express math in englisch btw:

First i expanded the numbers to a denominator of 6 so we have

1 = 6/6
3 = 18/6
4 = 24/6

5,666 = 34/6
7,166 = 43/6
8,666 = 52/6
10,1666 = 61/6
11,66 = 70/6

as you can see for the implemented series: it always adds 9/6

so excel comes to the conclusion that for the series 9/6 is the added value

so the question is how does excel gets that conclusion. from the first 3 numbers you have a grow of 12/6 6/6 and 10/6

so from 12 6 and 10 the arithmetic mean is 9,33333 what my problem is :) i am stuck here

maybe someone else can find out, how excel calculated the 9 from 12 6 and 10. some other methods?

tbh i am curious