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SD! :
About :
Registration :
Barcodes
Barcodes
Slave Registration Numbers (SLRNs) have 9 digits,
written as 3 groups of 3 - for example, 123-456-781.
(Until June 2005, six digit numbers were issued, and so 123454 became
000-123-454.)
The Slave Register
defines a way of encoding an SLRN as a standard EAN/UCC barcode,
of the type used in shops. We include 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
by machines,
and has the name "SLRN" in case the 3-groups-of-3 pattern isn't
distinctive enough.
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.
The marking slaves wiki
article suggests various ways in which slaves and submissives may be
tagged or marked with their Registration Number.
Many registrants have uploaded pictures with
their SLRN barcode on a tag or as a tattoo.
If you know an individual's number, then you can look up their profile and
certificate using the search profiles form.
For more about barcodes, see the EAN/UCC
website.
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