A charging post with its cable hanging in loops, a car park behind it. — PhotographRoger Starnes Sr, Unsplash

forecast

/ˈfɔːkɑːst/ noun

A statement about what will probably happen.
A promise that admits it might be wrong.

22 April 2026 · London · 1 minute

A weather forecast is the most widely read piece of statistics in the world, and most of its readers ignore the most important part of it: the probability.

Saying how sure

A forecast of arrival charge has the same form. It is a central estimate and a spread:

(1)

\hat{s} = s_{0} - \frac{1}{B} \int_{0}^{d} c (x) d x \pm σ

where $s_{0}$ is the charge at departure, $B$ the battery’s capacity, $c (x)$ the energy used per kilometre along the way and $σ$ the uncertainty, which grows with distance.

The spread is what makes the forecast honest.¹The same test is used for weather forecasts and is called calibration: of all the days given a 30 % chance of rain, it should rain on about 30 %.

Most of the craft is in $c (x)$ : slopes, speed, temperature, wind. Most of the trust is in $σ$ . A forecast that says 12 %, give or take 5 and lands at 9 has kept its word.¹

Being wrong well

Every forecast will be wrong. The question is whether it was wrong in the way it said it might be, often enough that the driver stops checking. See range.