refereeing senior League matches. Aston taught many courses, including a series that was recorded for novice referees. He called the series, "Refereeing is thinking." Aston refereed the 1963 FA Cup Final and the "Battle of Santiago", the match between Chile and Italy in the 1962 World Cup. FIFA Referees' Committee Aston did not referee any more games either in the 1962 tournament (having strained his Achilles Tendon), or in later World Cups. He was, however, appointed to the FIFA Referees' Committee for eight years, chairing it for four. He was in charge of all referees for the 1966, 1970, and 1974 World Cups. In 1966 Aston also introduced the practice of naming a substitute referee who could take over in the case of the referee being unable to continue for any reason (this eventually evolved into the practice of having a designated fourth official). He also successfully proposed that the pressure of the ball should be specified in the Laws of the Game. In 1974, he introduced the number board for substitutes, so that players could easily understand who was being substituted. He was also credited for the improvement of refereeing beginning with the World cup 1970 in Mexico through his efforts to bring about uniformity. Red and yellow cards Following an incident in the England vs Argentina match in the 1966 World Cup, it came to Aston's knowledge that Jack Charlton had been booked by the German referee, Rudolf Kreitlein. Charlton called the press office, where Aston was ensconced (as Head of World Cup Referees), in order to confirm the information that he had read within the newspaper that Kreitlein had booked him. Aston, driving from Wembley Stadium to Lancaster Gate that same evening, had Charlton's confusion in mind during the journey. On the trip, as he stopped at a traffic light junction at Kensington High Street, Aston realised that a colour-coding scheme based on the same amber/yellow ('stop if safe to do so') - red (Stop) principle as used on traffic lights would traverse language barriers and clarify to players and spectators that they had been cautioned or sent off. Aston later explained that upon arriving at his home, he explained the dilemma to his wife, Hilda. She disappeared into the other room, only to return a few minutes later with two "cards" made of construction paper. She had cut them to fit into his shirt pocket. Thus