Investors should keep an eye on the Value Line Geometric Index, after the major indexes hit fresh all-time closing and intraday highs last week.
While these records may have led some investors to "think the market is 'too stretched' or extended," Jonathan Krinsky, chief market technician at MKM Partners, explained in a note that the Value Line Geometric Index could suggest "the breakout could be just getting started."
"This [index] is actually just now at the same level it was at in 1998. So we've basically gone sideways for 18 years, if you're talking about the average stock," Krinsky said on CNBC's "Halftime Report."
The "equal weight" index holds 1,700 securities and is "one of the truest metrics of broad market breadth," said Krinsky. The advantage of looking at this index is that it "takes out the impact of some of the big cap stocks" and "provides a realistic representation of what the 'average stock' is doing," Krinsky explained.
Krinksy added that while the index is approaching an 18-year breakout, it's still "not quite there yet."