Men,
Frankly, we all know that most of us have people in our area who do not take the game as seriously as we do. For some people, I would recommend carrying a book with them, or as the FED Umpire manual says, to have one easily available.
For most of us, we would never tolerate someone bringing out the book to try and correct us, it may well be an ejectable offense. But I woulkd rather have somebody get the call right by having a rule book with them to refer to than messing things up.
Of course, having said that we need to also admit that coaches should never carry a rule book with them to a game, live hand grenades in the dugout can always blow a coaches hand off or worse, get him ejected.....