Quote:In this case, you take the last 4 digits of the lower barcode, 3 1 1 6

You now simply add 1 to the first number, 2 to the second, 3 to the third and 4 to the fourth.

So:
3 + 1 = 4

1 + 2 = 3

1 + 3 = 4

6 + 4 = 10

Any number that ends up greater than 6 can't be entered on the radio, so you simply subtract 6 from it. So in the above example, the last number is 10, which can't be entered so 10 - 6 = 4

The code in this example is 4 3 4 4