There are two classes of mouse buttons that are used in the COSMIC instrument window.
The first kind is used for the filter, aperture, object type, and grism menus. For these, click on the right mouse to bring up the menu, and then click again on the desired new filter, for example.
The second kind is used for the Guider Focus, Guider PA, and Base PA. For these, the three mouse buttons have different functions. When you point the mouse at the ``+ -'' bar, then the buttons assume the following functions: left mouse = ``+'' (increment); right mouse = ``-'' (decrement); middle mouse = speed toggle (fast/slow). For example, if you want to increase the base PA by a large amount, you move the mouse to point at the ``+ -'' bar in that part of the camera window, toggle the middle mouse until it shows ``fast'', and then hold down the left mouse until the angle has increased by the desired amount.