Locomotive check codes were used by the Southern to make sure that the correct car number was written down. Use the following steps to calculate the check code for any locomotive number.

1. Take any four-digit road number. Add zeros if front if the engine only had two or three digits.

2. Add the first digit, plus twice the second digit, plus the third digit and twice the fourth digit. If doubling exceeds a single digit result, like 2 x 8 = 16, then add the two digits; in this case, 1 + 6 = 7.

3. Take the sum and subtract from the next highest multiple of 10 (10, 20, 30, etc.) to give a one digit remainder.

4. Convert the one-digit remainder into a letter as follows: 0 = A 1 = F 2 = H 3 = J 4 = K 5 = L 6 = R 7 = T 8 = W 9 = X