These charts are used to determine long run value for commodities. As an example, this is a graph of LME Nickel from 1960 through 2018:
Here is how this works: The horizontal axis is the price of the commodity price in 2018$. It is adjusted for both inflation and the change in value of the $US. The vertical axis is the forward ten year return. So a dot on the graph, say from June 1999, is the price on June 1999 and the change in price from June 1999 to June 2009. Obviously this stops in 2008, since we don’t know forward ten year returns after that. The red vertical line is where we are now May 2018.
Note that the axes are on a log scale. Also note that the ten year return is expressed in fractions, not percentage. So a "2.0" means the price will be 100% higher in ten years.
This graph is forecasting that inflation-adjusted nickel prices have risen up to fair value. The forecast is for 10-year real prices to about remain the same.
BTW, this was a great trade. A year and a half ago, this graph was forecasting a doubling of long-term nickel prices. It has occurred.