[Figleaf23]

Some missing information might be useful to know. What is the TL, and why specifically six books?

But in anyway, let's consult the rule text for Gizmos:

You always seem to have just the
piece of gear you need. Once per game
session per level of this advantage, you
may pull out one small item of equipment
that you could have been carrying."

Okay, so that covers your book being the right one for any given occasion. The number of levels covers the frequency of availability, adjust as you perceive the need. The 'could have been carrying' element is no problem, but do note that it says 'small item', so personally I'm thinking that doesn't cover massive tomes, and I'd think that a standard textbook is a the very outside of 'small item' scope, if permissible at all. A Cosmic (Rules Exemption) modifier could address the size issue.

The text continues:

This “Gizmo” remains undefined
until you reveal it. It does not even
“enter play” until you take it out; thus,
it cannot be damaged, lost, stolen, or
found in a search.

So he doesn't need to specify the number of books. If he's going to carry six books anyway, your probably best specifying them and their contents so they might be useful without using up a use of Gizmo, and leave the Gizmo itself an undefined among the rest of the books.

A Gizmo must be small enough to
fit in an ordinary coat pocket, and
must meet one of three criteria:

1. An item you own but did not
specifically state you were carrying.
...
2. An item that you probably own,
and that is in keeping with your character
concept, but that is minor or
ignorable enough to leave unspecified.
...
3. An inexpensive device widely
available at your tech level. ...

Here's where we run into a little difficulty. I don't think this criteria 1 or 3 matches the stated need for this character. As to 1, the idea is that he doesn't have to know in advance what book to own. Regarding 3, any but the most pedestrian reference works can't really be called inexpensive, even at TL8.

That leave criterion 2. A reference book is in keeping with an academic character, certainly. Is it minor and ignorable enough to leave unspecified? I'd say yes, provided it's mundane to the setting. The sticking point is, however, 'probably own'. A lawyer probably owns legal references, an archaeologist probably owns archaeological references, but is it likely that each would own the other? Not really. I think to allow a Gizmo to cover this situation you have to be somewhat liberal with the concept of 'own'. For example, a professor generally has privileges respecting his university's library, and might be interpreted to be sufficiently probable ownership. Or, the character could be a Wealthy intellectual, presumed to have a large private library as part of cost of living.

As to pricing Gizmo to limit it to reference books only, we've seen that that would eliminate two of the three criteria, so arguably its a reduction of -66.7% right there, before you even consider the further restrains within criterion 2. Following this thinking, an -80% end point is not unreasonable.