When the AppleScan software is launched, it calculates the dimensions of
the main screen (the screen with the menu bar) in pixels. The AppleScan
software assumes that no screen is larger than the main screen, and so
does not allow a window to be resized larger than the main screen as would
be normal.
However, by holding down the COMMAND key while resizing the window, the
window can be resized to fill the SuperMac display.
(NOTE: This technique may work with other applications; however, it may
cause problems if the window is resized larger than the software can
support.)