full reporting number, except locomotives and multiple units destined for the Southern Region, which continued its long-standing practice of two-character alpha-numeric displays. By 1976, the replacement of the huge number of manual signal boxes with centralised power-signalling coupled with computer-based train control and more modern telecommunications systems meant that it was no longer necessary to display headcodes throughout the railway network. Outside the Southern Region blinds were set to 00 or 0000, and discs/lamps to the former express passenger code. Roller blinds were later blanked or plated over to show two dots and new trains introduced for service outside the Southern Region after this time usually had no train reporting number display equipment. Many trains intended to run over Southern Region lines were designed to display the numeric route-code portion of the train reporting number, which they still display, usually as a dot-matrix display. Components The main purpose of the headcode is to assist the signaller in routing and regulating the train correctly, and it is especially useful if services are disrupted. After the introduction of the four-character codes, originally it was intended for signallers to visually note the train by the number displayed on its front; with the coming of automated systems the number has been retained internally within timetables and signalling systems but with some exceptions detailed above is no longer displayed on trains. Train classes For operational reasons, certain trains have priority in running. To help operating staff, they are grouped into classes; these were formerly identified using letters. When the letter groups were replaced by numerals on 18 June 1962, the classifications became: (formerly A) Express passenger, newspaper, or breakdown train; express diesel car; snow plough on duty; light engine proceeding to assist disabled train. (B) Ordinary passenger, branch passenger or "mixed" train; rail motor (loaded or empty); ordinary passenger or parcels diesel car; breakdown train not on duty. (C) Parcels, fish, fruit, livestock, milk or other perishable train composed entirely of vehicles conforming to coaching stock requirements; empty coaching stock (not specially authorised to carry Class A code). (C) Express freight, livestock, perishable or ballast train pipe-fitted throughout with the automatic vacuum brake operative on 90 per cent of the vehicles. (D) Express freight, livestock, perishable or ballast train with not less than 50 per cent vacuum braked vehicles piped to the engine. (E) Express freight, livestock, perishable or ballast train with 20 per cent