I have a pivot table with one column that contains average percentage values.

The grandtotal shows "29.62" but I don't know how this is calculated as it's not the average of the sum of that column otherwise it would be "29.58" (591.52 divided by 20)?

Average % value
29.29
29.04
28.81
29.01
29.23
29.09
29.18
29.30
29.17
29.01
29.58
29.89
29.56
29.50
29.43
30.30
31.22
31.11
30.01
29.79
29.62