The Southern Railway used check codes to confirm that the correct road number was reported.  You too can figure out the check code for any road number.

1. Take any diesel road number.  Add zeros to the beginning of the number if the it only had a two or three digit road number.  For example, road number 2750.

2. Add the first digit, plus twice the second digit, plus the third digit and twice the fourth digit. If doubling exceeds 9, like 2 x 7 = 14, then add the digits; in this case, 1 + 4 = 5.

3. Sum the 4 individual numbers, then take the number in the "10" spot, the right most digit.  In this example, the sum is 12, the right most digit is "2". Subtract that number from 10.  For our example, this would leave you with "8".

4. Convert the number into a letter using the following table: 

0 = A, 1 = F, 2 = H, 3 = J, 4 = K, 5 = L, 6 = R, 7 = T, 8 = W, 9 = X

In this example, the check code for 2750 is "W".

Now you can look up any number with this code form: