Burndown chart

A line of work remaining against time across a sprint — falling toward zero if the sprint is on track, flat or rising if it is not — read every day, not at the end

The horizontal axis is days, the vertical is whatever the team estimates in. The straight line from the start to zero is the ideal; the real line's distance from it is the conversation at stand-up. A burn-up chart is the same story told as work done, which also shows scope being added.