Hi Pete,

"...Other than opening MPCORB.dat and manually removing the selected
asteroids, and then doing an Edit Comet Data from Guide itself, is
there some way to prevent the display of asteroids that I've already
observed so that I may more easily spot those that I haven't?

I'm afraid not. I've thought about providing something like
this (a means to flag "show me only this subset of asteroids",
or in your case, "_don't_ show me this subset"). But right now,
the only filtering is magnitude-based.

Incidentally, you _can_ edit MPCORB.DAT in a text editor and
remove the lines of the offending objects. They will then
disappear. You won't need to play around with Edit Comet Data
at all. So I shouldn't say "you can't do it". I should say
"you'll need to do a bit of text editing."

One advantage of this approach is that if (as I suspect) you're
just interested in the brighter asteroids, you can edit MPCORB.DAT
and delete all but the first few thousand lines. This will cause
Guide to run quite a bit faster. After the first few thousand
objects, you get into pretty faint territory.

-- Bill