From the Toolbar: Find the Arc Start-Middle-End Tool icon on the Entity Toolbar (color coded blue) and Click on the tool. The tool is now active and ready for use.

 
From the Shortcut Key: The default shortcut key for the point tool is the letter "Shift + A, 1". Simply press the key and the tool will be activated.

 
From the Command Line: Type "arc_start_middle_end" into the command line, at the top of the Notification Window, and press the Enter/Return key.

1. Click on the drawing to specify the start point of the arc.

2.  Move the mouse and click on a point you desire to be on the arc but is not the same as the start point. This is the middle point.

3.  Move the mouse and click on a point you wish to designate as the end point. This is the position the arc will run to and stop.

Reset:

To add an arc entity from user supplied data using the (Start-Middle-End) method open the Tool Tab in the property tree.

1.  Type the start point coordinates into the "Start Point" 3D Point Property Field found on the Tool Property Tree and press Enter to accept. This will position the starting point for the arc.

2.  Type the middle point coordinates into the "Middle Point" field and press Enter to accept.

3.  Type the end point coordinates into the "End Point" field and press Enter to accept. This will finish the arc creation process.

Reset:

Escape (Esc): Cancels current tool and activates the default tool (Selection Tool).

Space: Resets this tool.