回归法的自由度 (DF)
用于得到拟合线的点数量（
2 个）。DF 用于确定 p 值。
相关图表工具
常用统计图形在线生成工具：
Pareto Chart
Bar Chart
Box Plot
Histogram
Line Chart
Scatter Plot
Time Series Plot
Function Grapher
Normal Distribution Graph
Normal Probability Plot
实用工具：
Calendar with weeks
Public Holidays by Countries / Regions
Timer & Countdown
Date Calculator
World Clock & Time Zones