Apple’s Mac sales fell (IDC) or grew (Gartner) last quarter by Philip Elmer-DeWitt @FortuneMagazine July 11, 2012, 11:50 PM EST E-mail Tweet Facebook Google Plus Linkedin Share icons U.S. market shares. IDC (top) and Gartner (bottom). Click to enlarge. FORTUNE — In separate reports on the state of the worldwide personal computer market issued Wednesday, Gartner and IDC agreed about one thing: The quarter that ended in June was a miserable one for traditional PC vendors. Gartner called the market “flat.” IDC’s term was “stalled.” Both reported a decline in global shipments of 0.1%. Both attributed it to a variety of factors: The sluggish economy, buyers waiting for Microsoft’s MSFT Windows 8, the fact that Intel’s INTC Ultrabooks haven’t yet taken off, a general lack of interest in PCs. As Gartner’s Mikako Kitagawa put it: “Consumers are less interested in spending on PCs as there are other technology product and services, such as the latest smartphones and media tablets that they are purchasing.” It’s when you drill down into the details that discrepancies arise. In the U.S. market, for example, IDC singled out Lenovo as the only top tier leader that managed to maintain positive momentum, growing shipments 6.1% year over year to put itself in fourth place after Hewlett-Packard HPQ , Dell DELL and Apple AAPL . In Gartner’s report on the same market, however, Lenovo doesn’t even make the list of the top five vendors and Apple, rather than seeing its Mac sales drop 1.1% in the quarter (as IDC had it) actually grew them 4.3%. One used to be able to explain the discrepancies between Gartner and IDC by the fact that Gartner reported shipments to end users and IDC reported shipments into channel (i.e. distributors). But IDC now describes its numbers as representing “shipments to distribution channels or end users” (emphasis ours) and Gartner doesn’t specify what its numbers mean. Gartner does note, however, that its data include “desk-based PCs and mobile PCs, including mini-notebooks but not media tablets such as the iPad.” The two firms agree about that. In their world, netbooks and Ultrabooks are PCs, but tablets are not. If they were, Apple would be the world’s largest vendor — by far — not HP. Below the fold: IDC’s and Gartner’s worldwide numbers.