Is This Unusual? A Value Against Its Normal Range

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Opens on Chapter 18’s example: the headline’s “hottest October day in five years”: 84°F, against thirty Octobers of Ines’s records.

The new value

Years in the record, for the record check

Past values comma-separated

A change from last period

This period

Earlier periods, in order the last one is last period

Enter your numbers, then press Calculate.

How it works

Count how many past values were at least as high: if it’s a third of them, the new one is ordinary. With no trend at all, each of n years has the same 1 ÷ n chance of being the highest, so short records break often. For a change, compare it with the past changes: if many were bigger, this one is inside the usual wobble.

From the book, Chapter 18. In thirty Octobers the hottest day reached 84°F or more 12 times (40%); the middle October peaked at 83°F. In a five-year record any year has a 20% chance of a record by luck. Library visits up 6% in a month: 8 of the last 24 monthly changes were bigger. Every chapter and its calculator →

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