Why Apple's stock is down, pushing market value below $1 trillion

The world's most valuable company was a lot less valuable Friday, as a disappointing earnings report from Apple sent its shares tumbling and its total market value below $1 trillion. 

Apple's sales in its latest quarter and its estimates for the holiday season surprised experts. The tech giant also shook investors by saying it will no longer disclose the number of iPhones it sells each quarter. 

Shares fell $15.86 to $206.36, or a decline of 7.1 percent, in Friday trading, pushing its market capitalization to about $996 billion. A company's market value is calculated by multiplying its current share price by the total number of shares investors hold.

In August, the tech giant became the first $1 trillion publicly traded U.S. business, a milestone reached after it boosted revenue on higher-priced models such as the iPhone X. Yet just three months later, the company spooked investors by announcing it wouldn't disclose the closely watched iPhone sales figure. 

"The tech giant announcing that it will no longer be announcing product unit sales only made investors all the more nervous, if sales were expected to be good surely you would want to show the figures?" noted Fiona Cincotta, an analyst at CityIndex, in a research note. 

Apple was unique among big smartphone makers in saying how many phones it sold and what the average price was. Apple gets most of its revenue from iPhone sales and lately it's boosted its profits by selling higher-priced models.

The unexpected change raised suspicions that Apple might be trying to mask a downturn in the phone's popularity. The company says the quarterly numbers and prices didn't necessarily tell investors how strong its business has been.