Using the mouse wheel
Depending on the settings, you can use the mouse wheel to adjust line thickness, focus, or toggle between line thickness and focus:
Recording line thickness
Adjusting the cursor size enables you to record the line thickness (i.e., process diameter) used to trace:
- Rotate the mouse wheel.
 - To display the thickness of the line in the tracing window, click Trace>View>Thickness. 

 
Focusing
- Click the icon in Move>Z axis>Mouse wheel focus. 

 
OR 
                                                - Check Focus with mouse wheel in the File>Preferences>Movement>Mouse wheel section.
 
This will disable the Adjust Cursor Size default action with the mouse wheel.
The easiest way to navigate in the Z orientation one plane at a time is to use the Page Up and Page Down keys on your keyboard.
Enable both line thickness recording and focusing with the mouse wheel
- Check Focus with mouse wheel in the File>Preferences>Movement>Mouse Wheel section to change the mouse wheel action to focusing.
 - Rotate the wheel while holding down Ctrl to adjust the cursor size to match the line thickness.