Ah, but the statement "the plane of its swing remained constant" is not imprecise; it is false. And I don't mean false-but-kinda-true like "pi = 3.14" is false-

Ah, but the statement "the plane of its swing remained constant" is not imprecise; it is false. And I don't mean false-but-kinda-true like "pi = 3.14" is false-but-kinda-true; I mean just plain wrong. The fixed-plane idea seems to be a common misunderstanding, even among intelligent people, but it ain't so. The plane turns, even with respect to a "fixed" frame of reference that does not rotate with the Earth. I would have been better just to say that the plane changes, showing that the Earth rotates, and leave the explanations for another time.