"From my perspective, this is the heart of earnings season. How earnings trends are developing is top of my mind," said David Lefkowitz, senior equity strategist at UBS Wealth Management Americas.
"The market wants to see the good earnings data is not just about financials," he said.
Apple, the largest S&P 500 stock by market capitalization, is the highlight of Tuesday's earnings reports. Analysts polled by Reuters on average expect the iPhone maker to report earnings of $1.65 a share on revenue of $46.89 billion for the quarter.
"Tech is the largest sector in terms of an earnings weight," Lefkowitz said. "Getting a better handle on trends there is going to be important. We've seen some weakness in industrials. [We] want to see how broad-based that is."