UIPACK by default maintains a small (3 line) scroll region at the base of the
terminal screen for prompts and for normal FORTRAN output. However this region
is erased each time a text Viewport is updated (this being a consequence of the
VAX/VMS Screen Managment Package) so that multiple viewport operations are
relatively inefficient. The Application Programmer may set this scroll region
size to zero, thus inhibiting its update, but having the side-effect that normal
FORTRAN output to the screen may corrupt the screen image.