Umpiring library?

[Thane Yennie]

At the risk of being frowned upon by my colleagues I will ask this very simple question.

What texts (rules reference and mechanics) should I have in my library? Like many others who are on this board I am trying to improve my craft and would like to know what are the minimum references to have at hand.
At the present time my library includes:
The 2001 edition of the Babe Ruth rule book & casebooks
The NAPBL (before it changed to PBUC - is there any new information in the PBUC that is not in the NAPBL?)
Umpire's Guide Book Vol. II - Mark Ambrosius
Smart Baseball Umpiring - George Demetriou

From what I gather the J/R and JEA are not available, yet many rules interps are presented from these two sources. Any help is greatly appreciated.