From 1980 to 1999, the Dow gained against gold, from a ratio of about one Dow point per oz. to 42 points per oz. Then for twelve years, the Dow declined against gold, but recently the stock market has gained, as the Dow surged & gold dropped. The ratio is now 10.5.
The Dow might be undervalued in gold at 10 times & overvalued at 20. Should the ratio return to 20, the Dow might go to 18,000, while gold could fall to $900. Gold at $2000 & the Dow at 40,000 seems less likely, but in that case maybe a ratio of 10 for a Dow of 20,000.