Error Spread Explorer: Why Rough Guesses Multiplied Together Land Close

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Opens on Chapter 9’s example: four guesses, each off by a factor of 2 either way.

Number of guesses

Each could be off by a factor of

Count it close if within a factor of

When the errors all lean the same way

Every guess too big by a factor of

Load another example from the book

Enter your numbers, then press Calculate.

From the book, Chapter 9. With two guesses, 50% of the combinations cancel exactly. With four there are 16 combinations, and 14 land within a factor of 4. With ten there are 1,024: 65.6% land within a factor of 4 and 89.1% within 16. If all four lean 20% high, they don’t cancel: the answer is 2.07 times too big.

Rounding is half up, the way the book rounds. Numbers can be typed as 1,450, $38, 12%, 1/20, 2.5 million or 3 × 10⁷. Everything stays in your browser: no sign-up, nothing stored or sent.