Key functions in GUI mode

+ or = zoom in
- zoom out
* zoom to extents
Home go to the top sheet
Delete or Backspace go to the next higher sheet in hierarchy
PgUp go to the previous sheet in sequence
PgDn go to the next sheet in sequence
Tab toggle between old and new revision
? or H open/close help window
D when comparing revisions, show difference
N show newer sheet
O show older sheet
Q quit the viewer