The long-term strategic objective remained the gaining of step-by-_step access to the luxury segment of the market, the most important factor in upgrading the Audi marque being the car's advanced technology, which put it among the pioneers in contemporary automobile engineering. In January 1971 the first double-page advertisement appeared containing the slogan which has since been so closely associated with the Four Rings: 'Vorsprung durch Technik' - 'The Technological Edge'. The importance of technical research and development was confirmed in August 1969, when Audi began to build its own technical development complex at Ingolstadt. The initiator of this project was Technical Director Dr. Ludwig Kraus, who succeeded in convincing Wolfsburg that an independent Audi development centre was needed. Subsequent events proved him right, and much of the creative work produced at Ingolstadt was also suitable for Volkswagen models. The Audi model range developed rapidly, initially around the original four-stroke car which became known as the Audi 72 (based on its engine power). Later versions were the 80, Super 90 and 60, and at the end of 1968 the 72 and 80 were replaced by a new Audi 75. Meanwhile, Ludwig Kraus had a clear picture of how he felt a new Audi 100 should look, but as new model development was regarded as a VW prerogative his only chance was to advance the development of the new car in secret. It slowly took shape in this clandestine fashion until the clay model was 'accidentally ' discovered in the styling studio by Board Chairman Rudolf Leiding.