Comment by geor9e

"each possible ticket number follows a pattern: add 11, except add 4 if the last digit is 6…Only God knows why"

That pattern feels suspiciously like how a tacked-on modulo check-digit would act.

It seems the real citation number, x, excludes the last digit, and you only needed to +1 increment to it.

Then they tack on a last digit, a check-digit, of (x+1) mod 7. That would be the same pattern.

The contract for the system does have the clause "validate the data transcribed from handwritten Citations…a check-digit algorithm to control errors in the Citation number field" https://www.sfmta.com/sites/default/files/reports-and-docume...