Briefly |
With a scatter plot active, choose the line you want from the Graph menu. |
Fathom lets you add several kinds of lines. Be sure the graph is active. Then you can select various lines from the Graph menu:
Movable line. You get a line you can adjust with the mouse. Its equation appears. Drag the middle to move it up and down; grab the ends to rotate the line and change its slope. (Note: you can also add a movable line to a function plot.)
Least-squares line. You get the least-squares linear regression line, its equation, and the value for r^2.
Median-median line. You get the median-median line and its equation.
If your scatter plot data line up more-or-less in a line, or there is an important line (such as a limit) in the graph, you may want to know the equation for the line in order to make good predictions. Often, the slope or the intercept of the line are meaningful in the situation.
How to calculate least-squares slope and intercept.
How to find the median-median line.
Note: These three commands also appear on a scatter plot's contextual menu. Right-click (Windows) or -click (Mac) on the graph to see it.