Overview:  

PosiCode is a "position" based symbology, while most single width symbologies are presence/absence symbologies. Presence/absence symbologies are constructed by considering each character as a series of rectangular modules which may be either white or black. Each bar consists of a filled-in (black) rectangle and each space consists of one or more empty (white) rectangles. As a consequence of this approach, the bar width is usually specified to be the width of one module. A position based symbology, on the other hand, de-couples the widths of the bars from their positions. The centers of the bars are specified to be laid out on a grid of equally spaced parallel lines. The distance between these grid lines is called the G-dimension and is analogous to the X-dimension of conventional bar codes.  

Two variations of this code are allowed: PosiCode A, and PosiCode B. PosiCode A is optimal for applications where: 1) the mark width approaches the resolution of the reader, or 2) the accuracy of mark placement cannot be well controlled. PosiCode B is optimal for applications where the mark width must be larger than the G dimension (between 1G and 2G), due to limitations of the marking technology. 

The characteristics of PosiCode are: 

Encodable Character Set:

All 8-bit values can be encoded.

-  The default interpretation shall be (a) for values 0-127, ANSI X3.4 (i.e., ASCII) and (b) for   values 128-255, ISO 8859-1: Latin Alphabet No. 1. This corresponds to ECI 000003.

-  4 non-data function characters

-  5 code subset selection characters

-  1 start character

-  1 stop character

-  1 check character

• Code type: Continuous
• Elements per symbol character: 6, comprising 3 bars and 3 spaces. Bars are all approximately equal in width. Space widths are defined based on center-to-center distances between bars. Center-to-center distances range from 2-9 for PosiCode A, and 3-10 for PosiCode B. Check character: 12 elements comprising 6 bars and 6 spaces. Stop character: 7 elements comprising 4 bars and 3 spaces.
• Characters Self-checking: No
• Symbol Length: Variable
• Bidirectionally Decodable: Yes
• Symbol Check Character: One, mandatory
• Data Character Density: 9 or 13 modules per symbol character (PosiCode A), 12 or 16 modules per symbol character (PosiCode B).
• Non-Data Overhead: Equivalent to 35 modules (PosiCode A), or 48 modules (PosiCode B)