how to count vertices and edges from the faces alone, and why there are exactly five
Built as a memo rather than a table: the thing worth hanging it up for reads across the room, with the full reference in smaller type below it.
Three sizes in one archive — from a sheet on the fridge to a poster on the wall.
A Platonic solid is a convex polyhedron whose faces are all the same regular polygon, with the same number of them meeting at every vertex.
Put a dot in the centre of every face of a cube and join the dots on neighbouring faces: you get an octahedron, and the face centres of an octahedron give a cube back. The cube has 6 faces and 8 vertices, the octahedron the other way round, 8 faces and 6 vertices, and both have 12 edges.
The dodecahedron (12 faces, 20 vertices) and the icosahedron (20 faces, 12 vertices) pair up the same way, and the tetrahedron pairs with itself: 4 faces and 4 vertices.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 4 independent checks before it is allowed to build — how many items there are, the order they come in, and the claim in the highlighted box itself. If one fails, there is no file.
the IWF colour code and the plate count: from target weight to each side of the bar, no calculator
why a “yes” from a test that is right 99 times in 100 is wrong more than nine times in ten when one in a thousand has the thing
the first digit of a number: why a one turns up more than six times as often as a nine, and in which sets that is true
how many people it takes for two of them to share a birthday — and the same count for codes and fingerprints