Notice how the bars of the 3 and 5 are embedded in the bars of the 8 and 2. Codabar is a discrete bar code. You can pull apart characters into discrete, individual units. The spaces between characters do not have critical dimensions. A check digit is used to check that the data is read correctly.
Different symbologies apply different formulas to the encoded numbers to yield a single digit.
That digit is the check digit. That check digit is usually added to the end of the already encoded numbers. The computer checks that the numbers were read correctly by comparing the check digit it calculates against the check digit it read. Reading a check digit of 392 and calculating a check digit of 392 from the other numbers it read, the bar code reader now is doubly certain that the numbers were correctly decoded. Bar code technology is millions of times more accurate than typing when it comes to entering information into the computer.