In English the unit is an automatic shuttle unit or automatic reversing unit. The German, I assume, is a compuond noun of automatic pendulum?
Well yes and no. I don't know how to explain. Our compound words always have on main component and one (or more) describing ones. Take a "Haustür", house door. Door/Tür is the main part, Haus/house the describing one as it also could be a sheds door (Schuppentür) or the door of a fridge (Kühlschranktür).
Here "Automatik" (automatic) is the main part and "Pendel" (shuttle) the describing one. So "pendulum automatic" or "shuttle automatism" to me sounds more closely to our "Pendelautomatik". An "automatic pendulum" to me sounds as if a pendulum (main component) would work on its own (automatic beeing the component describing the pendulum).
jj:P.S. Would ledge/sill/cill make any difference? Nontheless, After careful consideration I just decided not to swap my attic for a windowwhatsoever
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P.P.S. Would automatic and automatism have the identical meaning in English?