You can enter your own equation for a fit curve (define custom fit) and add the resulting line of fit to your graph. To add a custom fit curve to a plot in Grapher, see the steps below:

1. Select the plot you wish to add the fit curve to.
2. Click Graph Tools | Add to Graph | Custom Fit  (in Grapher 14 click Home | Add to Graph | Fit Curve | Define Custom Fit).
   
3. In the Add Custom Fit dialog, specify your custom fit equation and parameters, and click OK.

To edit any aspect of the fit curve, you can select the fit curve in the Object Manager and then edit the Fit equation and Parameters on the Plot tab of the Property Manager.

To add a custom fit equation to a plot in Grapher 13 and earlier versions:

1. Select the plot you wish to add the fit curve to.
2. On the Plot page in the Property Manager, click the Add/Edit button in the Fit curve field.
3. In the Fits dialog, click the Define button.
4. In the Define Fit Equation dialog, specify your custom fit equation, parameters, and name, and click OK.
5. In the Fits dialog, select your custom fit curve from the Available Fits list and click the Add button.
6. Click OK.

To edit any aspect of the fit curve, you can select the fit curve in the Object Manager and then click the Edit button in the Edit equation field of the Plot page in the Property Manager to reopen the Define Fit Equation dialog.

Updated March 2023