Friday

"New chart," Wren says. "Warm-up minutes across, lap time up. 7 runners from the log."

Comet plots the dots. "They go down. More warm-up, faster lap. What do you notice?"

"A negative slope," Wren says. "-0.38. Each extra warm-up minute goes with about 0.4 fewer minutes of lap time."

"And the intercept is 9.68," Comet says. "A lap time of about 9.68 minutes with no warm-up at all, by the line."

Nova projects both charts side by side, one rising and one falling. "Would you like a hint? The sign of the slope tells the direction."

"Positive climbs, negative falls," Comet says. "Same tools, opposite story."

"Our fun run poster can show both," Wren says. "Practice helps, warm-up helps, and a line says by how much."

Lines of fit show up anywhere two numbers move together: a steady walk, a growing plant, a draining tank.

The slope's sign tells the direction. Positive means y rises with x. Negative means y falls as x rises.

The slope's size tells the rate, in the data's units. The intercept tells the starting level at x = 0.

Always ask whether the intercept means anything. Zero strides, zero seconds makes sense. Zero weeks of practice is a stretch.

The crew's falling line is lap time = -0.38 × warm-up minutes + 9.68. Every number is the crew's own Run Log reading.

A full week of lines. Tomorrow is Track Day: a family scatter plot and a line of fit from your own home.