If you type the word “calculator” or enter an equation into the Google search bar, a basic calculator will show up if you hold your smartphone in the upright “portrait” position.

That brings back some very fond memories. I was in 6th form in school doing double maths and physics A-level (in the UK – that’s about 17 years old) and bought a Sinclair Scientific by mail order.

Figure 1 HP-35 power supply (courtesy of Kees van der Sanden). Not wanting to wait till I had time to build a proper solution, I threw together a LiPo battery “holder”, and for the last year, I’ve ...