Additional functions may be found, such as zooming in/out or various application-specific tools. Depending on the GUI, the size of the thumb can be fixed or variable in size; in the later case of proportional thumbs, its length would indicate the size of the window in relation to the size of the whole document, indicated by the full track. While proportional thumbs were available in several GUIs, including GEM, AmigaOS and PC/GEOS, even in the mid 1980s, Microsoft did not implement them until Windows 95. A proportional thumb that completely fills the trough indicates that the entire document is being viewed, at which point the scrollbar may temporarily become hidden. The proportional thumb can also sometimes be adjusted by dragging its ends, such as in Sony Vegas, a non-linear video editing software package. In this case it would adjust both the position and the zooming of the document, where the size of the thumb represents the degree of zooming applied.