- 1). Add together every other digit in the number sequence, starting with the first digit. For example, if you have the number sequence "0123456," add together 0, 2, 4 and 6 to get 12.
- 2). Multiply the result by 3. Using the example from Step 1, you should get 36 (12 multiplied by 3 is 36).
- 3). Add together every other digit starting with the second digit. Using the example from Step 1, add together 1, 3 and 5 to get 8.
- 4). Add the results from Steps 2 and 3. Using the example from Step 1, you should get 44 (8 plus 36 is 44).
- 5). Round the result up to the nearest multiple of 10. Using the example from Step 1, round 44 up to 50.
- 6). Subtract the result in Step 4 from the result in Step 5. The difference is the check digit. Using the example from Step 1, you should get a check digit of 6 (50 minus 44 is 6).
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