One of the problems of making a portable product in pre-LCD days was the power draw of the LED display. Sinclair got round that by using a pulsing power supply.
For Sinclair it was one of his most satisfying inventions, because, he says: “What we did there was to make an extremely slim one - ours was only nine millimetres thick and everybody else was making great clunky things - much bigger than ours - and we managed to reduce the power consumption by a factor of between ten and thirty times because we could switch the chip on and off without it losing its data, so it was only on for very brief periods. So we got the power consumption right down, so we could run it off these little tiny button cells. Nothing like that existed in the world and so we sold it very well in the US as well as over here."