FORTUNE -- As predicted, the headlines reporting Apple's (AAPL) quarterly earnings last week -- and the market's immediate and violent negative reaction -- failed to take into account that Q1 2013 had one less week Q1 2012. Even Tim Cook did lousy job explaining it.
"Apple's fiscal quarters are usually 13 weeks in length and always end on a Saturday. Every 5 or 6 years, depending on the number of leap days in the multi-year period, Apple adds a 14th week to its first fiscal quarter to align fiscal quarters closer to calendar quarters. On a weekly basis, Apple's revenue was $4.2 billion in the recent December quarter versus $3.3 billion in the prior-year period. On an equal week basis, revenue in the quarter rose 26.7%"
What Leitao is too polite to mention is that the companies that make up the S&P 500 grew their revenue a comparatively anemic 3.8% in the same period, according to Capital IQ, and that without Apple's contribution that growth would have been even lower.
Yet the trailing PE ratio of the average S&P stock is 17.5, and in the past week the market -- driven in large part by computer algorithms that respond to "sentiment" (i.e. headlines), not fundamentals -- has pushed Apple's trailing PE down to 8.6.
The extra week is only one of a several subtleties in Apple's Q1 2013 that seem to have gone over most reporters' heads. A sample from Leitao's Thursday post:
"Most observers look to the income statement to determine the company's growth," Leitao writes in summary. "However, Apple's balance sheet that accompanied the December quarter revenue and earnings numbers tells a much different story. It's not so much that Apple's rates of growth have declined, it's an issue of discovering where the current rates of growth are reported."
His post is titled The Mysterious Case of Apple's Missing Growth. As reader Jim Neal put it, "This piece is so full of stuff that nobody's talked about in the past week it's not funny."
Thanks to Neal and to Apple Insider's Daniel Eran Dilger for spotting it.
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