Slave Registration Numbers
The Slave Register (TSR) was created in 2000 to provide slaves and submissives with a unique Slave Registration Number (SLRN).
Numbers have 9 digits, written as three groups separated by hyphens - for example, 123-456-781. This pattern of digits and hyphens helps make the SLRNs more distinctive and less likely to be confused with other numeric identities, such as telephone numbers. Until June 2005, 6 digit numbers were issued, and so 123454 became 000-123-454. Over 225000 registration numbers were issued by TSR between 2000 and July 2016. A registration certificate for each number is displayed on the TSR website, and can be found with the look up form on the main page.
TSR defines a way of encoding an SLRN as a standard EAN/UCC barcode, of the type used in shops. TSR includes one of these barcodes on each registrant's certificate, and its format is very similar to the barcodes used for books. In the marked-up diagram on this page, we've marked the different pieces that make up the barcode.
At the top is the SLRN in the 3-groups-of-3 form, separated by hyphens. This
part of the barcode is intended to be read by people rather than scanned
and has the name "SLRN" in case the 3-groups-of-3 pattern isn't
When using a scanner, the thick and thin lines of the barcode itself are read by the machine from left to right to obtain the number: it's as if the scanner takes a slice through the lines, and most scanners will still work if the direction of the scan isn't perfectly at right angles to the lines.
At the bottom of the barcode is a longer, 13-digit number - the number actually encoded in the lines. This number is printed along with the barcode in case the scanning fails, so it can be manually keyed in by the operator. (You may have seen shop assistants having to do this occasionally.)
This longer number includes the SLRN as its last 9 digits, but starts with the 4 digit prefix 2672. That prefix is within the range defined by EAN for businesses' internal uses: organisations are free to use these numbers in any way they choose, and you won't find a book or a box of washing powder in a supermarket with one of those numbers.
The SLRN then follows, this time without any hyphens. The final digit of both the SLRN and the longer barcode number is the checkdigit, and is calculated from the preceding digits. Scanners can do the calculation themselves and display an error if it doesn't match the value in the barcode. You can use the checkdigit to validate SLRNs even if they're not included in a barcode, by adding the 2672 prefix and doing the checkdigit calculation.
If you're interested, the rule is add up the values of the odd numbered digits (1, 3, 5, ..., 11), then add on three times the values of each even numbered digit (2, 4, 6, ..., 12). Then take the last digit of this sum, subtract it from 10, and then take the last digit of what's left as the checkdigit.
If you are printing or engraving barcodes, then the recommended width is the standard 31.25mm of an EAN-13 barcode. Barcode scanners should be able to cope with images between 80% (25.1mm) and 200% (62.5mm) wide though.