How many Macs did Apple sell last quarter? by Philip Elmer-DeWitt @FortuneMagazine July 15, 2015, 5:50 PM EDT E-mail Tweet Facebook Google Plus Linkedin Share icons The Mac continues to zig as the Windows PC market zags. According to IDC’s preliminary estimates, released last week, sales of Macs grew 16% year over year while sales fell at Lenovo (-7.5%), HP (-10.4%), Dell (-8.7%), Acer Group (-26.9%), Asus (-7.7) and Other (-19.7%). If those numbers hold up, it’ll be quite a coup for Apple and the Mac. But that’s a big if. (More on IDC’s track record below.) Our panel of Apple analysts is not quite as optimistic as IDC. Most are expecting Mac sales to grow year over year, but of the 23 we’ve heard from so far—12 professionals and 11 amateurs and independents—only one (FBR’s Daniel Ives) came in with numbers anywhere close to IDC’s. IDC preliminary data put last quarter’s Mac shipments at 5.136 million. The average estimate from our panel was 4.83 million, and it ranged from a low of 4.5 million to a high of 5.2 million. We’ll find out who was closest to the mark next Tuesday when Apple reports its fiscal Q3 2015 earnings and publishes its quarterly Mac sales number. Below: The individual analyst’s estimates — pros in blue, indies in green. Thanks as always to Posts at Eventide‘s Robert Paul Leitao for pulling together the Braeburn Group numbers. About those IDC Mac sales numbers: They date back to October 2014, when Apple broke into IDC’s list of the top five PC makers worldwide for the first time, and they haven’t been right yet. Last quarter, when Apple dropped out of the top five, IDC was off by at least 815,000 units. We asked IDC’s Loren Loverde how this could be. “Shipped vs. sold can be part of the difference,” he replied by e-mail. “Another important part is that the numbers you’re pulling from our press release are preliminary. While IDC’s methodology for final data will account for earnings and in-country distribution checks, some of those are not available for the preliminary data, so we supplement with supply-chain data (components, assembly numbers, etc.). Those have a higher margin of error.” Follow Philip Elmer-DeWitt on Twitter at @philiped. Read his Apple AAPL coverage at fortune.com/ped or subscribe via his RSS feed.