Roc:
Let's say you're a carpenter, and you want to break up 8 feet into an a certain number of parts. Hmm, 2 parts, that's easy, 4 feet each, and a nice reference mark at 48 inches. How about 3 parts? That's easy, too: 32 inches, again a nice multiple of 16, again nicely marked. What about 4 parts? Why that would be 24 inches, also, a nice mark every two feet. Wow, this is pretty easy. I could break it into 6 or 8 parts pretty easy, that's every 16 inches (again, nicely marked) and every 12 inches (ditto), respectively. But how do you quickly lay out 5 parts in eight feet? Black diamond. (7 parts would also be hard to do, but 5 is a much more useful divisor.) I believe this is also the standard in some areas for metal stud spacing. You are now a fully trained journey-person, and can get people to buy you drinks.
OK, now back to turret discussions.