William Playfair put the first line charts of trade into his Commercial and Political Atlas in 1786: years along the bottom, money up the side, imports and exports drawn as two lines you could watch cross. When he came to Scotland he had a problem. The records weren’t there. He had one year of figures, and a line needs at least two points before it can go anywhere. So he drew the one year as a row of bars, a pair for each country Scotland traded with, and apologised for it in the text: a chart like this, he said, takes in no portion of time and is much less useful than the others. The bar chart, which now turns up in every quarterly report there is, started as a workaround for a gap in the data, written up by its inventor as the weaker method. Sometimes the thing you’re sorry about is the one that lasts.