Identification number of a container consisting of prefix & serial number and a check digit e.g. MOLU 123456; number in bracket is check digit. The check digit provides a means to verify the correctness of the owner code and the serial number. Check digit can be deduced by a particular method of calculation. However summarising: The first digit represents the length of the container.[ 2 for a twenty feet container & 4 for a forty feet container]; the second digit represents the height of the contained; 0=8' container | 2= 8'6" TEU | 3 = 8'6" FEU | 4 is more than 8'6" | 6 = 4' high container.