# Calculate Check Letter for Rollingstock and Locomotives

## Instructions

Enter the vehicle class and number into the fields above.

If you're calculating a check letter for a loco which has no class letters (i.e. 830, 930, 44 class etc) then leave the Vehicle Class empty

For vehicles that just have a name enter the first 4 letters of the vehicle name in the vehicle class field and put 0 as a vehicle number

## How it works

Excerpt from "Code and Practice For the Defined Interstate Rail Network"

2.4.2 The check letter should be determined in accordance with the following procedure:

1. Alpha characters are allocatd a numerical value according to their position in the alphabet, viz A = 1, B = 2, C = 3, ..., Y = 25, Z = 26
2. Leading zeroes are instered if necessary between the alpha group and the number to form a 9 character vehicle classification.
3. Assign numberical values to each character to form a sequence a1, a2, a3, a4, N1, N2, N3, N4, N5, where a1 to a4 correspond to the vehicle class and N1 to N5 refer to the vehicle number.
4. Calculate the value of the following series: (1 * a1) + (2 * a2) + (3 * a3) + (4 * a4) + (5 * N1) + (6 * N2) + (7 * N3) + (8 * N4) + (9 * N5)
5. Divide the sum by 23 and add one (1) to the remainder to give the position of the check letter in the alphabet. A check letter character of I is to be recorded as X, and O is recorded as Y.