information is protected from errors with a BCH code, and two complete copies are included in each QR symbol. The message dataset is placed from right to left in a zigzag pattern, as shown below. In larger symbols, this is complicated by the presence of the alignment patterns and the use of multiple interleaved error-correction blocks. The general structure of a QR encoding is as a sequence of 4 bit indicators with payload length dependent on the indicator mode (e.g. byte encoding payload length is dependent on the first byte). Note: Character Count Indicator depends on how many modules are in a QR code (Symbol Version). ECI Assignment number Size: 8 × 1 bits if ECI Assignment Bitstream starts with '0' 8 × 2 bits if ECI Assignment Bitstream starts with '10' 8 × 3 bits if ECI Assignment Bitstream starts with '110' Four-bit indicators are used to select the encoding mode and convey other information. Encoding modes can be mixed as needed within a QR symbol. (e.g., a url with a long string of alphanumeric characters ) [ Mode Indicator][ Mode bitstream ] --> [ Mode Indicator][ Mode bitstream ] --> etc... --> [ 0000 End of message (Terminator) ] After every indicator that selects an encoding mode is a length field that tells how many characters are encoded in that mode. The number of bits in the length field depends on the encoding and the symbol version. Alphanumeric encoding mode stores a message more compactly than the byte mode can, but cannot store lower-case letters and has only a limited selection of punctuation marks, which are sufficient for rudimentary web addresses. Two characters are coded in an 11-bit value by this formula: V = 45 × C1 + C2 This has the exception that the last character in an alphanumeric string with an odd length is read as a 6-bit value instead. Decoding example The following images offer more information about the QR code. Variants Model 1 Model 1 QR code is an older version of the specification. It is visually similar to the widely seen model 2 codes, but lacks alignment patterns. Differences are in the bottom right corner, and in the midsections of the bottom and right edges are additional functional regions. Micro QR code Micro QR code is a smaller version of the QR code standard for applications where symbol size is limited. There are