Deja Vu

As mentioned, the inventory recorded in the office computer and the inventory actually in the yard are different. These discrepancies occur because the same basic problems with the yard board model exist in the passive-tracking system:

• There are the normal keying errors associated with a computer system. These errors are analogous to the incorrect placement of a representation on the yard board. To correct the keying problems, more and more checks are identified and added to the computer system to keep incorrect entries from being made.
• The computer becomes a model of the container yard. In essence, the yard board model is being built inside the computer. In fact, the computer checks easily exceed those performed using the yard board model Ñ a more perfect model of the container yard is being built. Eventually, this results in a tight system that will only accept exactly correct data. These checks will eventually serve as a frustrating trap for the keyboard operator.
• As with the paper system, the basic cause of the discrepancies is unreported container moves. For example, a particular problem occurs toward the end of working a vessel. When trying to get the vessel off berth, other containers are moved indiscriminately to get the last few required on board.

These basic inventory errors then produce a multiplication of similar errors. For instance, inventory errors in the computer cause planners to produce incorrect work lists for the equipment operators. The equipment operator places the container at a convenient location close to the one requested by the planner [see Figure 5]. If the operator diligently records the change on the work list, the changes to the work list can be batched into the computer later. Unfortunately, even if recorded, many of these changes will be lost. They are lost because other inventory errors, along with tight computer checks, cause the computer to reject the entry of the corrections to the work list. The frustrated CRT operator will simply give up and ignore the corrections.