Apple store. Image source: The Motley Fool.

Apple's (AAPL 1.27%) fiscal fourth-quarter earnings have just been scheduled. After market close on Thursday, Oct. 27, the tech giant will announce its quarterly results and host a live conference call to discuss its recent performance. As the quarter that marked the iPhone 7's release, investors are likely interested in these results.

Ahead of the earnings release, here's an early look at what to watch.

Revenue

One key area to watch when Apple reports earnings is revenue. Apple has reported year-over-year declines in revenue for two quarters in a row and expects another drop in Q4, management said when it reported Q3 earnings. Specifically, it guided for revenue of $45.5 billion to $47.5 billion, representing an 11.7% to 7.8% dive compared to year-ago fourth-quarter revenue of $51.5 billion.

Apple's monstrous upgrade cycle for iPhone 6 in fiscal 2015 has made year-over-year revenue comparisons difficult since the product represents well over half of its revenue. In fiscal 2015, iPhone sales soared about 37% as consumers jumped on the opportunity to buy the first iPhones with larger 4.7-inch and 5-inch displays. But the iPhone 6s and 6s Plus, which sports the same form factor as the iPhone 6 and 6 Plus, have led to a comparatively lackluster upgrade cycle so far.

iPhone sales

While iPhone has been a key reason for declining revenue in recent quarters and likely will be this quarter as well, there is more uncertainty than usual when it comes to forecasting even a ballpark figure of where iPhone unit sales could land.

iPhone 7. Image source: Apple.

The uncertainty surrounding iPhone sales for Q4 is derived from several factors. First, Apple launched iPhone 7 toward the end of the quarter, leaving investors playing guesswork on how the new phone impacted sales. Second, Apple didn't announce first-weekend sales like it usually does. Third, the iPhone 7 launched a week earlier than usual and in more than twice as many markets.

Theoretically, these circumstances would suggest it's possible the iPhone 7 and 7 Plus could provide a year-over-year boost for the last few weeks of the quarter -- and potentially help moderate declining total revenue. Of course, as usual, deliveries of the new iPhone have been limited by supply, with delivery times for many of the iPhone 7 Plus models about a month out for buyers or order one today. All of these considerations shroud the new iPhone's impact on the quarter in mystery.

Apple's guidance for total revenue in Q4 suggests the company expected a year-over-year decline in iPhone unit sales -- even with knowledge of its plans to release iPhone 7 during the quarter. But could the iPhone 7 provide surpass expectations and provide a big enough boost to help mitigate some of this predicted decline?

For context going into this quarterly report, Apple delivered about 48 million iPhones in the fourth quarter of 2015.

Whatever Apple reports on Oct. 27, investors already have one thing going in their favor: The stock trades very conservatively, with a price-to-earnings ratio of just 13. This means Apple is essentially priced for continued headwinds when it comes to growth. Better-than-expected fourth-quarter results, therefore, would be icing on the cake.