12. So let me guess, the next diagonal—the 3rd parallel to the PD will increase by either 6 or 8?
The 3rd diagonal, starting with 15, increases by 6.
15 + 6 = 21
21 + 6 = 27
27 + 6 = 33 …
And, the starting number came from the difference (∆) between the PDs—one from above at the top of the column, and one to the right at the end of the row, both where they intersect the PD. PD 16 - PD 1 = 15.
TIP: The number (#) we are adding each time to the specific starting number is simply double (2x) the Axis number of that diagonal!