Copper is used in so many industries that its long term price is said to parallel economic activity, so Doctor Copper is a common title for copper itself.
I was playing around with various charts the other day, and was surprised to see a relationship of silver and gold to the Dow Jones INDU which I had never noticed, although the gold to silver ratio is often talked about as having historical significance. I turned the ratio upside down the other day on a StockCharts monthly line chart which shows only each month's ratio of the closing price of the constant forward silver price divided by gold's monthly close.
To my amazement, major lows in this monthly silver to gold price ratio were closely aligned with major lows in the Dow Jones INDU.
I've put arrows on the obvious major spike lows of the silver to gold ratio, but other lows in the ratio, as in 1985, 1995, 1997, and 1999 also were followed by meaningful Dow advances.
The current issue is the very low level spike in the silver to gold ratio in 2016 which was accompanied by the recovery of the Dow from the second 14% drop of 2015-16 "mini-bear market". Also the 2016 election low on the daily chart seems associated with the Dow up spike.
If this 2016 low results in Dow bull markets like those from 1982, 1990, 2003, and 2008, that would be a big surprise to the bears!