Interleaved 2 of 5 is based on Standard 2 of 5 symbology, but uses both bar and space width to encode information so the density of ITF25 is much higher. It is primarily used in the warehouse industry.
Interleaved 2 of 5 encodes any even number of numeric characters in the width of both bars and spaces.
It is called “Interleaved” because 2 characters are encoded in a unit of 5 bars and spaces. The even position character is encoded into bars whilst the odd position character is encoded into spaces. Thus, Interleaved 2 of 5 symbology can only encode data elements with even number length.
A typical Interleaved 2 of 5 barcode has the following structure:
A start character bsbs
Message encoded
A stop character bbsb
Start with the right-most digit in the message; mark the character with even and odd position. The right-most digit has the even position.
Sum all digits in the odd position;
Sum all digits in the even position, and then multiply by 3.
Add the result 2 and result 3;
Divide the result of step 4 by 10, the check digit is the result equal to that 10 minus the remainder.