RM4SCC is the name of the barcode symbology used by the Royal Mail for its Cleanmail service. It enables UK postcodes as well as Delivery Point Suffixes (DPSs) to be easily read by a machine at high speed.
This barcode is known as CBC (Customer Bar Code) within Royal Mail.
Royal TNT Post uses a slightly modified version called KIX which stands for Klant index (Customer index); it differs from CBC in that it doesn't use the start and end symbols or the checksum, separates the house number and suffixes with an X, and is placed below the address.
There are strict guidelines governing usage of these barcodes, which allow for maximum readability by machines.
They can be used with Royal Mail's Cleanmail system, as an alternative to OCR readable fonts, to allow businesses to easily and cheaply send large quantities of letters.
As the example below shows, the barcode consists of a start character, the postcode, the Delivery Point Suffix (DPS), a checksum character, and a stop character.
Encoding and checksum
Each character is made up of 4 bars, 2 of which extend upward, and 2 of which extend downward. The long bars of each half can be assigned weights of 4210 to produce a digit from 1 to 6. The combination of the top and bottom halves give 36 possible symbols: 10 digits and 26 letters.
|Top||Bottom (1=long bar, 0=short)|
The check symbol is computed by summing the top and bottom half values separately, modulo 6, and combining the final sums into a symbol. In the example above, the top half values are 26114512. This sums to 22=6×3 + 4. This the check symbol has a top value of 4. The bottom half values are 64224625, which sum to 31=6×5 + 1. The check symbol's bottom half value is 1, so it corresponds to the letter I.
- PostBar – Derivatives of RM4SCC used in other countries (inc. Canada, USA, Australia)
- "De KIX van TNT Post" (PDF) (in Dutch). TNT Post. January 2007. Retrieved 2007-07-17.
- Royal Mail Cleanmail manual
- tool + font – calculates the checksum character for a postcode and produces its RM4SCC barcode.
- check-digit explanation