Look at the bottom left corner of your checks. The first nine-digit number on the left is the bank routing number. Immediately to the right of that is your checking account number.
dig meaning, definition, what is dig: to break up and move soil using a tool, a machine, or your hands: . Learn more.
The dictionary meaning of the word Digress is 'to leave the main subject temporarily in speech or writing.' or simply deviate. As you say,I digress means  I am straying from the main subject right now. . Like in this sentence - 'I need to digress a bit to let the ink dry.'. Hope this helps :)