"What Is This Big Round Well-Type Thing In The Middle Of The Women’s Restroom? It’s In An Older Bathroom And It Doesn’t Seem To Have Any Water Running To Or From It… Just A Big Cylinder With A Drain In It"

Answer: "It's a sink. For washing your hands. You step on the ring to start the water."
Pretty sure you are wrong.... the black/blue pages in those are thin. photo looks more like an album.
Better... er... what? That would depend on the specific function of the slide rule. I used these in an engineering drawing office early 70's
#56... That is what is left after removing a metal screen that was painted at one time
came with firearm accesories... Probably a wick for old gun.
But the two things can look more or less identical.