# Southern Railway Locomotive Check Letter Calculator

Starting sometime in the mid-1970s, the Southern Railway began applying a single letter to the right of the road number on the cabs of their locomotives. This number did not appear in the numberboards, nor did it appear with any end numbers on locomotives that had them. The purpose of this number is to ensure accuracy when writing down the road number or entering it into a computer. The letter used was calculated from the road number using the formula detailed below. Enter a Southern road number into the box below to generate the correct check letter for that number.

The check digit is calculated as follows:

Double the second digit.

Double the fourth digit.

If either of these are greater than 9, subtract 9 from them.

Add the digits together.

Disregard the left digit of this sum. Use the letter from the following table based on the right digit of this sum:

1 = X

2 = W

3 = T

4 = R

5 = L

6 = K

7 = J

8 = H

9 = F

0 = A