Investors say there’s no one chart that will signal when the stock-market bottom is in. But technical analyst Chris Kimble argued Friday that an important tell could be offered by a commodity index that is testing a support level that has held for the past 40 years.

Kimble Charting Solutions

In a Friday blog post, the founder of Kimble Charting Solutions pointed to the chart above for the Thomson Reuters Equally Weighted Commodities Index, which he said “will go miles and miles towards telling us if we are headed towards very tough times or if the huge declines of late are actually in a bottoming process.” The chart tracks the index on a monthly basis back to 1954.