Apple's key earnings report is coming up Tuesday.

The company is set to report fiscal first-quarter results after the closing bell, four weeks after it lowered revenue projections for the period, pouring cold water on the stock. Earlier this month, Apple adjusted revenue estimates to $84 billion, down from a previously stated range of $89 billion to $93 billion. Shares tanked 10 percent but have since clawed their way back to trade essentially flat for 2019. Its share price Tuesday morning also was little changed.

The company will be disclosing some metrics for the first time, and omitting others when it reports results for the December quarter. Any surprises in the first-of-its-kind report out of Apple could shift the stock, which has seen unusual volatility in recent months.

Shares have lost 30 percent of their value since the company's last earnings report in November. The company's market valuation is now more than $250 billion less than the record $1 trillion it reached in August.

Here's what investors will be focusing on when Apple reports: