Aztec Code is a special space-saving version of Aztec
for encoding shorter messages (up to 95 characters).
Space is saved by removing one set of rings from the finder
pattern, eliminating the reference grid, and using a shorter
mode message which limits the symbols to four data layers;
otherwise, the encoding rules are generally the same as for
standard Aztec Code. Small Aztec symbols are completely decoder
compatible with standard Aztec symbols so the two types can
be intermixed in applications.
There are four possible sizes of Small Aztec symbol. As
with standard Aztec Code, the one and two layer symbols
employ 6-bit codewords for error correction while the three
and four layer symbols employ 8-bit codewords. Although
the 4-layer symbol holds 76 codewords, at most 64 of those
can be data words, thus Small Aztec symbols are limited
to encoding 512 bits of data (typically about 95 characters
or 120 digits).
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