HERE COMES THE BIG ONE: Apple reports its most important earnings in a long while

This is the big one, folks.

Apple will report its holiday quarter earnings after the market closes on Tuesday afternoon.

This will be the most important Apple earnings report in as long as we can remember.

Analysts across the board are saying Apple's iPhone business is going to be negative for the first time in history during the first three months of this year.

We'll find out if they are wrong or right when Apple provides its revenue guidance during the report.

Apple is the iPhone company, so if iPhone sales are down on a year-over-year basis, then the whole company will be down on a year-over-year-basis.

Apple's been a monster growth story for a long time.

Two years ago, Apple delivered $57.6 billion in revenue for the holiday quarter. It's expected to deliver $76.6 billion in revenue for the 2015 holiday quarter.

But, it looks like it may finally be out of room to grow. Analysts are looking for revenue guidance of $55.7 billion, which would be a 4% drop - the first revenue drop in the modern history of Apple.

This is already "priced in" to the stock. Most investors have already sold in anticipation of a year-over-drop in sales.

As long as Apple's revenue isn't worse than expected, the stock price should be OK. Plus, Apple management will be able to use the earnings call as an opportunity to explain and give its own spin on what's really happening with the company.

No matter what happens, it's going to be the biggest business event of the day on Tuesday, so tune in!

Via the Bloomberg terminal, analysts are expecting the following numbers. Note that Apple's fiscal Q1 is October-December:

• Q1 EPS: $3.23
• Revenue: $76.6 billion (versus Apple's forecast of $75.5-$77.5 billion)
• Gross margin: 39.9%
• iPhone unit sales: 75 million
• Phone ASP: $674
• iPad unit sales: 17.3 million
• Mac unit sales: 5.8 million
• Q2 EPS: $2.24
• Q2 revenue: $55.7 billion