2 Each of the numbers calculated in step 1 is multiplied by 2position, where position is the exponent to base 2. Position starts at 0, from left to right. The following table shows the multiplication factors: Calculation step 3 If the final difference is 10, then the check digit becomes 0. To ensure that this does not happen the standard recommends that serial numbers should not be used which produce a final difference of 10; however, there are containers in the market which do not follow this recommendation, so handling this case has to be included if a check digit calculator is programmed. Notice that step (ii) to (v) is a calculation of the remainder found after division of (i) by 11. Most programming languages have a modulo operator for this. Attention should be paid to how it works in the language chosen; i. e. if it gives back the decimal rest or the integer rest in order to get proper results. 11 is used as divisor because a container number has 11 letters and digits in total. In step 1 the numbers 11, 22 and 33 are left out as they are multiples of the divisor. Example Practical problems In day-to-day business it happens that containers do appear which do not follow the ISO 6346 identification at all; however, they are fully CSC safety approved containers. Usually these are "shippers owned" containers (SOC), which means that they are not owned by the carrier but supplied by the cargo owners (shippers). They may have no registered owner code and no category identifier and have no check digit. It is advisable to follow ISO 6346 as the absence of a compliant identification code causes problems for both carriers and container terminals to correctly identify the equipment and properly deliver the cargo, because computer systems require ISO 6346-conforming naming and as such missing prefixes are invented. For example, YYYY at the carrier and XXXX at the terminal causes the equipment to mismatch. Moreover, since ISO 6346 identification has become a requirement in international Customs conventions (Customs Conventions on Containers and Istanbul Convention), many Customs Administrations have begun validating that containers are marked as per the standard. Size and type codes The codes are compiled of the following elements: First character, representing the length (coded) Second character, representing the width and height (coded) Third and fourth character indicating the type of the container