Check digits can effectively be used to determine that all of the numbers in a numeric data stream were entered. This method involves adding up the numbers in the data stream in order to determine the check digit. Consider the following number, 789. The check digit would be: 7+8+9=24=6. If a 7 an 8 and a 9 are not entered then chances are that the check digit will be incorrect. This method will not detect a transposition error. For example,if879 were entered, the check digit would still be 6.