A background grid helps readers quickly
grasp the trends. Remember algebra, slope and “rise over run”? Didn’t
think so. But you do need to know that the Y-axis equals the rise going
up and down vertically. What are you measuring? Th e stock market?
Rainfall? Daily traffi c? Th at’s your Y. Th e X-axis is always time or
“run,” running left (from the past) to right (into the future). In 3D, the
Z-axis pushes out towards the viewer.