how to solve without guessing: five techniques, simplest first, the search order and a 17-clue puzzle
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.
Fill in the digits 1 to 9 so that each appears exactly once in every row, every column and every 3 × 3 box. The given digits never change.
The puzzle on the big grid has 17 digits and exactly one solution. With 16 that never happens: in 2012 Gary McGuire, Bastian Tugemann and Gilles Civario published a proof. They searched every completed grid, up to symmetry, by computer and found none that 16 digits determine uniquely.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 3 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