The dials are used to control either the entire view or to move individual molecules. When no molecules are selected, the dials have the following interpretation:
X rotation o o X translation Y rotation o o Y translation Z rotation o o Z translation Slab o o Scale
The rotations and translations apply to the entire view.
Slab and Z translation apply to clipping and display with regard to the front and rear of the viewing box. Slab controls the size of the viewing box using units of the vertical dimension of window. When this value is changed by the dials, it is displayed in the window title. The z translation specifies the position of the molecule within this viewing box. Its value is also displayed with this dial is changed.
You can make the molecule completely disappear by either shrinking the viewing box down too small, or by z translating the molecules out of the box.
When some molecules are selected, then the interpretation is similar except that Slab and Scale have no effect, the translations and rotations apply to the selected molecules only. The origin of rotation can be set with the set origin menu item.