amplifier that was good in theory but sadly ahead of its time and available technology. The amplifier used low-frequency germanium transistors as pulse width modulators and switches and wrongly relied on the loudspeaker's inductance to filter the class D signal into audio. Most often this would short out the output transistors. When it did work the power level was far below 10 watts and Sinclair's main advertising channel, Wireless World magazine, was so deluged with complaints that it supposedly refused to take further advertisements from Sinclair. Sinclair Radionics launched the System 2000 amplifier, FM tuner and loudspeaker in 1968. followed by the System 3000 in 1972. Calculators and test equipment In 1972, Radionics launched its first electronic calculator, the Executive, which was considerably smaller than its competitors' by the use of hearing-aid-sized batteries. What had made this possible was it had been discovered that there was considerable latency in the display and memory and that, with the addition of a timer, power could be withheld from these battery-draining components for much of the time, thus greatly extending battery life. During the majority of the 1970s, Sinclair focused on building the most affordable pocket calculators with the best design. In 1972 Sinclair released the world's first slim-line pocket calculator, the Sinclair Executive, for £79.95. The calculator only included basic maths functions, and the LED display required much power. It is often credited as being the world's first attractively styled calculator that did not require mains power to be used like prior calculators. The Executive was a phenomenal success, earning Sinclair £1.8m in profit. In 1973 the slightly larger Sinclair Cambridge was introduced at a far cheaper price of £29.95 + VAT. A cheaper Executive was also launched shortly after. In addition to expanding the Cambridge range, the Sinclair Scientific was launched in 1975. It was a scientific pocket calculator for the very competitive price of £49.95. In 1977 a revised model, the "Scientific Programmable", was released at £29.95. The Scientific Programmable Mark 2 was later released, reducing the price to £17.22. In 1975, Sinclair Radionics launched the Oxford range of briefcase calculators. Sinclair also attempted to capture the top-end calculator market with the Sinclair Sovereign, available in plated gold or silver. The calculator was critically acclaimed for its excellent engineering and design and enjoyed short success. Final attempts at the mass-market for calculators, the Sinclair Enterprise and the President, did not