Published July 11, 2018
For faster processing, the banking industry began assigning routing numbers to represent the institution from which the funds should be drawn. The routing numbers are eight or nine digits and aid in the processing of paper, wire, and electroinic transactions. When present, the ninth digit is a "check" number to ensure that the other eight characters were processed correctly.
Typically, the routing number will appear as a machine-readable set of digits at the bottom of the check, before the account number on personal checks, but will also be represented in something called the "fractional number" at the top center of the check. Typically the fractional form is not required and will contain only eight digits.
When checks were first made machine readable, the data transfer was through the use of magnetic ink with less precision than current optical character recognition (OCR) practices; the check digit ensured more accurate processing.