The cycling coach at a sports school keeps her whole season on one sheet of squared paper, and she fills in almost none of it.
At the start of the season — week zero, before the first training block — her rider covered 20 kilometres in the week. In week ten she covered 80. Those are the only two numbers the coach wrote down before she picked up a ruler, put a dot at each of them and joined the dots with a single straight line.
«Two points are enough,» she says, when a new assistant asks where the rest of the data is. «If the training is working, the weeks in between are already on that line.»
They mostly are. Sixty kilometres of increase, spread evenly over ten weeks, is six kilometres a week, and the rider's actual weekly distance in week five was 50 — which falls on the line exactly. Week six was 55, one kilometre off, and the coach has drawn a small circle round it and written «wind» in the margin.
The straight line does two jobs. It smooths the noise of any single week — a cold morning, a puncture, a school exam — and it makes a prediction that can be tested: at this rate, week fifteen should be 110 kilometres.
The coach is careful about that second job. A line drawn through two dots will happily run off the top of the page, she says, and no rider improves for ever. The line is a rough plan, not a promise. What it is very good at is showing, in one glance, the week when a rider stops keeping up with their own rate of progress.