Can anyone point me to a resource or explain how serial numbers are arranged on 32-note sheets? To start, I understand the arrangement pattern of serial numbers and plate positions.
For example, this uncut sheet:
https://i.redd.it/bdwj1ay65qpz.jpgA1 has a serial number of 98088XXX and an "increment" of 60 (thousand). Going from A1 to H1, A2 to H2 ... A4 to H4, 60,000 is added to each serial number.

Here is another uncut sheet sample:
https://i.ebayimg.com/images/g/ox4A.../s-l1600.jpg. In this case the "increment" is 20,000.

What I'd like help understanding is how the increment number is determined. Surely it is mathematically based on the first five digits, but how?