Today I learned what the numbers on the bottom of my checks mean.
I was having a discussion with Tony about the long string on numbers at the bottom of our checks. I knew that some part of it was the account number, but wasn't exactly sure about the rest. It turns out the collection is very logical.
The first set of numbers on the check is the American Banking Association routing number. The routing number consists of 9 digits: AAAABBBBC. AAAA is the Federal Reserve Routing Symbol (mine indicates things go through the Federal Reserve Bank in St. Louis), BBBB is the institution identifier (which is specific to my bank), and C is the Check Digit (used to verify the accuracy of the other numbers).
The second set of numbers is the account number, and the third set is the individual check number.
After we figured that out, we moved on to a related question: why is the first set of numbers on the deposit slip different from the one on the check if it's going to the same account? It turns out that question has a logical answer, too. If a bank has a dedicated location that only process deposits, it will have a different routing number.
Now I know.