I was watching Crash Course Astronomy and came across a sentence with the word "setup" that I cannot get.(The sentence is at about the 4th to 5th minute of the video.)
At one perihelion pass, one side of Mercury faces the Sun. Then, 88 days later or so, it approaches perihelion again. But it's spun 1.5 times, and this means the exact opposite side of Mercury faces the Sun at this closest approach. 88 days later, Mercury has spun 1.5 times again and the whole thing repeats. It turns out it is a perfectly legitimate stable configuration, just like the one to one spin/orbit setup.
I have looked up all the meanings of "setup" in various dictionaries, but still I cannot understand what it means there. The first definitions to come up were "arrangement" and "organization", but at that moment it was still unclear to me whether that definition fit.