the Model 150 Cleaning Ensemble. However, new to Model 65, and slightly later in Britain on the 652A, was the introduction of a switch which automatically shifted the motor to a higher speed as the converter was inserted. The Convertible, or the Senior, in Britain, remains Hoover's worldwide bestselling cleaner. Although the domestic line was finally discontinued in 1993, a version called the Guardsman is still available in the commercial sector. 1963 saw the introduction of the Dial-A-Matic in the US – sold in Australia as the Dynamatic, and in Britain as the Convertible. This was the first-ever clean-air upright cleaner. The clean-air principle is similar to the flow of air through a cylinder/canister cleaner. Rather than the dirt passing directly through the suction fan and being blown into the bag, it passes through the bag first, leaving only clean air to pass through the fan. This principle was soon adopted by many manufacturers and continues to be used today. Also, the machine was constructed out of hard plastic. Hoover produced this cleaner from 1963 until the late 1970s in America. In the summer of 1969, Hoover further refined the Dial-A-Matic's design when they launched the 'Powerdrive' self-propulsion system on the Hoover model 1170. This idea took much of the effort out of pushing the cleaner, because, by using a system of gears, wheels, and belts, the cleaner used its own power to drive itself forward and backwards, the speed and direction being controlled entirely by the user though the 'Triple-Action' handgrip. The powerdrive feature on the model 1170 was so efficient, the user could push the bulky machine forward with one finger, and the feature could also be disengaged with a button on the handgrip so the machine could travel easily from room to room with the motor turned off, the machine was very difficult to push when the motor was turned off and the powerdrive was still activated. This was also the first vacuum cleaner available commercially that used the self-propulsion system. This extra technology made the Dial-A-Matic even heavier than the original and more expensive, at around $150 ($ today). The 'Powerdrive' system was carried over into the Concept range in 1978. The powerdrive system was later renamed "Self Propelled". Hoover continued to use this feature on many products of the 1980s and 1990s. It is still being used today by Hoover and numerous other companies. In