Clever and/or knowledgeable economists (aka: those who understand from the Austrian school rather than the Kensian school of voodoo economics) often call copper prices “Doctor Copper”.
Copper is so widely used in construction and fabrication that orders for copper fall just before the rest of the economy falls.
Your first lesson in Austrian Economics is that supply and demand determine prices. Thus a price plummet in copper is a clear indicator that the rest of the economy will be right behind as if attached to the sinking ship with an unbreakable anchor chain.
Hang onto your hats …
Put your seat and tray in the upright position …
Here we go …