"chrisv" <chrisv@nospam.invalid> wrote in message
news:rebiu3pcseavscittnkse33pnqs30trac4@4ax.com...

>>CRT monitors are designed to have about a 1/4 inch of blank display all
>>the
>>way around the picture.
>
> Since when? Ideally, the image shoud cover 100% of the usable area.
> (Of course, the tube itself is larger than that.)

That all depends on what you define as the "usable area," and
whether or not the opening in the monitor bezel encroaches on
that area.

In most CRT specs (the tube itself, not the monitor), there is a
"recommended image area" which is smaller than the full extent
of the phosphor screen. In part, this area is determined by what's
going on re the curvature of the inside of the glass faceplate as you
get to the edges of the tube (obviously, at some point that inner
surface is no longer anything even remotely resembling "flat," and
the geometry, etc., starts to go bad quicky in those regions. In
part, the area is also determined by the performance of the yoke
(at least a "typical" yoke as expected for that tube type, the focus
electronics, etc., convergence, etc., also going away as you get
close to the extreme edges. For monitor tubes, this results in
the optimum image area being somewhat smaller than what you
might expect from just looking at how big an area the phosphor
covers.

TVs are a bit different in that they are commonly "overscanned" -
i.e.., the scanned image actually extents beyond the edges of the
phosphor screen by about 5-10%. This basically hides edge
geometry and other problem by placing them where the viewer
can't possibly see them.

Bob M.