Coding and AI classes in Hemel Hempstead

The learner types Herring's 26 fine paper sizes into Python, converting fractions like 13½ into decimals, and works out each aspect ratio, the long side divided by the short. Then comes the folding function: halve the long side and swap if needed. For Foolscap, 17 by 13½ inches, the ratio starts at 1.259; fold it and it jumps to 1.588; fold again and it returns to 1.259. The sheet keeps flipping between two different shapes, so a folded Foolscap page never looks like a small Foolscap.

Algebra explains it. If a sheet has ratio r, folding it gives ratio 2 divided by r. The shape stays the same only when r equals 2 divided by r, which means r is the square root of 2, about 1.4142. Of Herring's 26 sizes, only Super Royal comes within 2 per cent of it. The learner then builds the modern answer: a sheet of exactly one square metre with sides in the ratio root 2 measures 1,189 by 841 millimetres, and halving it four times gives 297 by 210 millimetres, the familiar A4 page.

The final step is data checking. Herring lists "Double" versions of some sizes, and the program tests whether each is really two of the original laid side by side. Double Foolscap, 27 by 17, is exactly two Foolscaps. Double Post is within 2 per cent. But Double Pot has four times the area of Pot, and Double Elephant only 1.66 times Elephant: the names are traditions, not rules. The learner writes tests for the fold function, including that a root-2 sheet returns its own ratio.

Making sure a picture keeps its proportions through the code is the kind of care that makes programming worth learning in Hemel Hempstead in 2026. The longer argument is in why teenagers should still learn to code in 2026.