Apple's (NASDAQ:AAPL) first fiscal quarter of 2014 is an important one. In fact, on the strength of its new iPhone and iPad lineups, Apple has guided to report higher revenue during the quarter than ever before. For those tuning into the report and the earnings call on Monday, here are some metrics to watch and some benchmarks to compare them to.

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iPhone sales
iPhones are the most important driving factor in Apple's business results. They account for more than half of Apple's revenue and an even larger portion of its profits. Even more, Asymco's Horace Dediu has estimated the gross profit margin on Apple's iPhone to be at about 48% -- considerably higher than Apple's overall gross profit margin of about 37%. With so much of the company's business depending on iPhone sales, this number is the most important number to watch.

How many iPhones could Apple have sold during the quarter? Analyst estimates for iPhone sales, collected by Fortune's Philip Elmer-Dewitt, range between 50 million to 60 million units. The average estimate is 55.3 million, about 16% more units than the year-ago quarter. 

iPad sales
Apple's second largest product segment measured by revenue is the iPad segment. iPads accounted for 16.5% of Apple's revenue in its most recent quarter. Sales for the product are expected to be robust during the quarter.

Apple CEO Tim Cook predicted in the company's fourth-quarter earnings call that it was "going to be an iPad Christmas." Multiple studies have suggested that Apple is, indeed, seeing a lot of success with its new iPad lineup during the holidays.

Analysts estimate iPad sales for the quarter to come in around 21 to 28 million, with the consensus at 25 million -- up about 9% from the year-ago quarter.

Gross profit margin
Apple's gross profit margin will especially be a hot topic when it reports earnings on Monday. With its quarterly gross profit margin reaching peak levels in the first calendar quarter of 2012 of 47% and then plummeting to today's levels around 37%, deteriorating profitability is largely considered a central driving factor behind the decline of Apple's stock price from highs just above $700.

Apple guided for a gross profit margin between 36.5% and 37.5% in Q1. That would put the median guidance at 37%, 160 basis points below the year-ago figure and flat sequentially. Asymco's Horace Dediu predicts Apple to report a gross profit margin of 37.1%.

Could there be a surprise factor?
Since January 2013, when Apple changed how it provides guidance, there has been less will room for a surprise factor when the company reports quarterly results. Since the change, Apple's guidance has been incredibly accurate. So, investors shouldn't expect major surprise factors on the upside or downside -- though it would also be wise not to rule it out as a possibility (albeit an improbable one).

For reference, analysts expect earnings per share of $14.32 and revenue of $57.9 billion, on average.

To tune in to the earnings call, mark your calendar for 5:00 PM EST and go to this link.

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