When Multi Gage first appears "Mouse Mode" is enabled. This allows you to make selections using the Multi Gage arm in a similar fashion to using a mouse.
Using the arm you can do the following:
Enable/Disable Mouse Mode: This is done by pressing the left button. When "Mouse Mode" is disabled you can take hits with your probe.
Move the Pointer: Moving the last two axes of the arm up, down, left and right controls the mouse pointer's location. This may take a little bit of practice to effectively control the mouse pointer.
Right-Mouse Click: Press the right button to right-click on the interface at the mouse pointer location.
Left-Mouse Click: Press the middle button to right-click on the interface at the mouse pointer location.