How to read, in pieces, across a very wide line, eg 432 chars?

[dkcombs@panix.com (David Combs)]

Easy enough to read the left end, or the right end, but the
stuff in between is just about impossible to see.

So, how to sort of "tab" your way across it?  (Maybe
that's the answer: redefine tab to be 120 chars, and
indeed tab across.  But how to back up "two tabs"
to again see that already viewed part of the line?

One place you get these super-wide lines is when copying
and pasting a series of amazon reviews into an emacs
buffer.  Each paragraph in a review pastes (yanks) in
as one *WIDE* line.

And to save vertical space on the screen, you do NOT
want to M-q (fill) the thing.  

In fact, you might
have to successive paragraphs, each existing within an 
emacs buffer as a super-wide string, almost identical strings (obviously
a contrived situation), and you want to "tab across"
the WHOLE BUFFER, so you can look at corresponding
parts of two WIDE lines.


So, I'd like to march across the line, or sometimes the entire screen
of such lines, in maybe 80-wide pieces if in a
90-wide window (so each piece has some overlap at its start and end).

Ideas?

Thanks,

David