The town council met to decide whether to keep funding the evening bus. A slide went up on the wall showing passengers in two years, one bar beside the other, and the second bar was nearly twice the height of the first.
Somebody said it looked like the service had almost doubled. Several heads nodded.
The council's treasurer asked to see the figures rather than the picture. The first bar was ninety-five thousand passengers. The second was one hundred thousand.
The axis did not start at zero. It started at ninety thousand. So the visible part of the first bar stood for five thousand passengers and the visible part of the second stood for ten — which is indeed twice as tall, and tells you nothing about the two totals.
Nobody had done anything dishonest. The slide had been made by a clerk using the default settings of a spreadsheet, which fits the bars to the data and starts the axis wherever it likes.
The real increase was about five percent. Whether that justifies the funding is a fair question, and the council spent an hour on it. But it is a different question from the one the picture had suggested.
The treasurer asked for one change to the town's rules, and got it: every chart in a council paper must either start its axis at zero or say, in words, where it starts.