1. Click on the Line/Scatter Plot in the Object Manager to select it.
2. Click Home | Add to Graph | Fit Curve. By default, a linear fit will be applied.
3. Click on the Linear Fit in the Object Manager to select it.
4. In the Property Manager, click on the Plot tab.
5. In the Fitted Plot section, uncheck the box next to Apply fit to entire plot.
6. Update the Minimum plot value to fit (or Minimum date/time if the values in the data file are formatted as date/time).
7. Update the Maximum plot value to fit (or Maximum date/time if the values in the data file are formatted as date/time) with the x values for the range of data you would like to use.
   
   For example, if you want to limit the equation to the red area in the graph below, type in 40900 for Minimum plot value to fit and 40945 for the Maximum plot value to fit.

After changing the fit curve Fitted Plot properties, your fit curve will be reduced to the area in red.

9. To get the equation of the line:
   
   1. Click the Linear Fit plot.
   2. In the Property Manager, click on the Plot tab.
   3. In the Statistics section, set the desired Number format and Significant digits of the numbers in the equation, then click the button next to one of the commands.
      • Clicking on the Copy button in the Copy to clipboard field copies the information to the Windows clipboard for pasting into Grapher or another program.
      • Clicking on the Display button in the Display report field opens a text window in Grapher with the fit curve information.
      • Clicking on the Insert button in the Insert into plot document field allows you to click in the plot document window and have the fit curve information displayed as an editable text object.

Updated February 25, 2020