...huh. That's quite unexpected as the tower bonus is a matter of wind density while the books are a skill/knowledge aid, but if that's so...
@BoneyM, are there any commonly expected tasks where the Dusk and Dawn tower bonus and
ulgu book bonus would stack, or where the books would count but the tower would not? Have books been entirely obsoleted by the construction of that tower?
Almost everything where I had expected the book bonus to apply is something where the tower bonus would, and if they don't stack there seems no point in buying books on our Wind ever. We'd have to get the full book bonus from
five culture groups to match the tower which is functionally impossible since most cultures don't even have a tradition of using the Grey Wind.