The Automatic Curve Fit command will fit one of a list of functions to the selected region of a graph or table window. This command is available either by clicking the Curve Fit button  on the toolbar or by selecting it from the Analyze Menu.

To perform an automatic curve fit, highlight the region of interest by clicking and dragging the mouse across the graph. Choose Curve Fit from the Toolbar or from the Analyze Menu. If multiple columns have been graphed, choose the appropriate column from the list displayed in the pop-up box (This box will not appear if only one set of data has been graphed).

A reduced version of the graph will appear in the Curve Fit dialog box. Select Automatic under Fit Type. Select the General Equation you wish to examine, and click on Try Fit. (Coefficients are automatically applied, but can be adjusted. In this case, the Fit Type will revert to Manual). To examine other curve fit options, select the function and click on Try Fit. Click OK to close the dialog box and place the fitted curve on the main graph. A helper object containing the equation and fit coefficients of the fitted funtion will also be added to the graph.

Graphical Analysis chooses the best fit using a least-squares approach. The Mean Square Error is the sum of the distance squared of the difference between the fitted line and the data points, divided by the number of data points.  The curve with the smallest Mean Square Error is the one chosen.
 
 

See Also:

Curve Fit

How To/Curve Fitting