>How did André do this, with no tool but a pencil?

And paper, paper is the most important thing here. It is the extended human memory. The short term memory of human beings is extremely sort.

I use paper with color marker pens all the time for programming. Nothing beats paper right now. For doing the same thing on computers you need expensive gear like Ipads pro or surfaces and the useful surface is minimal.

I could use several A4s(normal paper size in Europe), A3s(double that), A2s(4 times that) A1 and A0. I increase the resolution using fineliners. It cost nothing compared with expensive gear.

When you are done you take a high res picture for archival. You can replot it if necessary or wacht it on TVs.