finding the week of any date with a pencil: the day of the year, the weekday and a division by 7
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.
Weekday numbers run from Monday (1) to Sunday (7). Shaded: days of January and the month of the example.
400 Gregorian years are 146,097 days, exactly 20,871 weeks. If every year had 52 weeks, 400 years would hold 20,800. The other 71 are all the 53rd weeks of the cycle. And the week-numbering year never strays more than three days from the calendar year: it begins between 29 December and 4 January.
Why the numbers can be trusted. Every countable number here is computed from data rather than typed in, and the sheet must pass 2 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