When the mouse pointer is over a button or menu, the usage information of that command is displayed both in a textual popup and in the status bar.
Since version 0.17, the status bar also shows the mouse navigation modes, and the orbit style.
The status bar shows the zoom level in the right corner, next to the mouse navigation style. The zoom level gives the size of the current 3D view in appropriate units for the current scale, for example, millimeters (mm) or meters (m).
The status bar also shows the last pre-selected object (any object under the pointer is pre-selected) or element of an object (vertex, edge, face), and the coordinates of the mouse pointer when the last pre-selection occurred; this is useful to know immediately the coordinate of specific vertices in your shapes. The 3D coordinates update automatically as long as the mouse pointer floats over a geometrical element; the update stops when the mouse pointer rests over an empty space in the 3D view.