On the blackboard, Professor Yi used red chalk to draw a pattern that looked very much like a candle. There was a standard rectangle in the middle, with a thin line extending above and below it, their lengths seemingly quite arbitrary.
Then the professor gripped his long, slender bamboo pointer and tapped the blackboard.
"This pattern is the basic component of a line chart: the chart line."
"This top point," the professor said, tapping the peak of the candle pattern's upper shadow with his bamboo pointer, "refers to the best thing that happened during the day; this bottom point refers to the worst thing that happened during the day."
As the pointer indicated them, two cloud-shaped explanatory diagrams appeared beside the upper and lower shadows, marking their respective meanings. Then the pointer shifted to the lower edge of the rectangle.
"This lower line is the time you got out of bed. At the same time, it is an 'eyes-open line' representing your overall state after opening your eyes."
"Correspondingly, this upper line is the 'eyes-closed line' for when you lie in bed and close your eyes to sleep."
"The eyes-open line, the eyes-closed line, the best thing, and the worst thing—these four dimensions form a complete, independent line chart."
"The line chart currently on the blackboard is red. That means that after opening your eyes in the morning, you might have encountered something unpleasant, but from that low point onward, your fortunes rose sharply until the best event of the day occurred, then gradually settled down, allowing you to fall asleep peacefully."
"Few people open their eyes in the morning and have everything go smoothly all day, with good things constantly happening, until they go straight to sleep at night without being affected by anything... But rare does not mean