In modern railway signalling practice each train is allocated a code which describes its type, priority and route. the code is displayed on a schematic display diagram in the signal box and enables the signalman to set up the correct route for the train to follow. the description code on the diagram automatically follows the movements of the train, and in addition, is transmitted to the neighbouring signal box when the train enters the adjoining area. the equipment used to display and manipulate these codes is known as a train describer, and the paper describes the first computer-based system to be brought into operation.