We know of solar-powered calculators, but here’s a unique proposition as it uses Faraday’s Principle of Electromagnetic Energy to power itself. All you need to do is shake this primitive number cruncher from side to side, enabling the magnet within to slide through the copper coil in order to generate electricity for your calculations. Should the numbers on the LCD display start to dim, just pick it up and shake it a few more times. Definitely a distraction in exam halls nationwide, but hey, if it helps save the earth, what’s forking out £9.99 for one of these?

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