pair of semaphore arms mounted on the locomotive – the angle of the two arms and their position (on the buffer beam or smokebox) indicated the routing. Train reporting numbers Historically train reporting numbers were used to denote trains in the internal working timetable. These contained one or more letters or numbers to either uniquely identify a particular train, or denote its route (particularly on busier lines). Not all lines used these and the details and extent of the practice varied widely between companies. Although these numbers were in many places confined to timetables and other documentation, in some busier areas they were actually shown at the head of the train. On the SR, a single alphabetic character system of denoting routes used on suburban lines grew into a two character route-based system. This was developed at the same time as a significant programme of electrification and the consequent introduction of a large number of multiple unit trains. Many of these trains were fitted with display devices to show the route code instead of a lamp or disc-based headcode. Originally this was a back-lit stencil with the single letter code, later a two-character roller-blind system was used. The code system had equivalence with the lamp or disc route-based headcodes in assisting signallers with routing trains. On the other railways, the reporting number was on occasion displayed at the head of the train along with the lamp headcode. This happened more often than not with special trains or other unusual trains (e.g. summer Saturday timetables), to allow signallers to identify unfamiliar trains and route them correctly. This code was sometimes either chalked onto the locomotive front or pasted as paper characters onto a headcode disc. The GWR sometimes used a three-character frame mounted on the locomotive smokebox in which the train reporting number could be displayed. After nationalisation, British Railways continued with these headcodes and the new diesel and electric locomotives and multiple units were built either with a disc/lamp system (now powered by electricity) or a two to four character roller-blind display system depending on what part of the network they were to work. 1960 headcode/reporting number merger In 1960, the current format was introduced where train class, route and reporting number information are combined in four characters. All diesel and electric locomotives and multiple units built after that date were fitted with a roller-blind display that could display the