41 and 42 for horizontal movement therealong as indicated diagrammatically by arrows 62 and 63 in fig1 inside the cabin 61 are not illustrated controls that can be manually manipulated by a human operator in order to control operation of the crane 11 several cables 64 extend vertically downwardly from the cabin 61 and have their lower ends detachably coupled to the container 12 the cabin 61 includes a not illustrated hoist arrangement that can effect vertical movement of the cables 64 in order to raise and lower the container 12 a cable position sensor is shown diagrammatically at 68 and produces an electrical signal that represents the vertical position of the cables 64 and thus the vertical position of the container 12 although the sensor 68 in the disclosed embodiment is a cable position sensor it could alternatively be any of a variety of other types of sensors including but not limited to mechanical optical electrical magnetic radio frequency and infrared sensors or switches a container tracking system includes a ground signpost 81 that is fixedly supported in approximately the center of the lower beam 29 on the inner side of the beam 29 the signpost 81 is a device of a type known in the art and is therefore described only briefly here.