[Oberon] SystemV - Viewer Scroll

[Andreas Pirklbauer]

   > Forward move seems favoured to backward in `Show' procedure,
   > that I do not understand yet.

One reason is that even though one knows the *position* in the source text (pos)
that one wants wants to scroll *to*, the *number* of lines (or, more general, the
scroll displacement dY) between that position (pos) and the current starting
position of the displayed text (F.org) is not known a priori. 

There are ways the address that of course. The benefit is to reduce/eliminate
flickering during continuous scrolling, but there is an extra cost to that..