Microsoft Reports Calculation Issue with Excel 2007

Microsofts Excel application—widely used by much of the business world—is having issues calculating numbers, but only in a dozen "very specific" use cases, according to the companys Excel blog on the Microsoft Developer Network site.

The problem was apparently introduced when Microsofts development team made changes to the Excel calculation logic in Office 2007.

The issues, according to the Redmond, Wash., software maker, are not in the calculations themselves—the result of the calculations stored in Excels memory are correct—but in the result that shows in the Excel sheet.

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"Said another way, =850*77.1 will display an incorrect value, but if you then multiply the result by 2, you will get the correct answer," wrote Microsoft team blogger David Gainer.

The Microsoft Excel team was alerted to the issue in Excel 2007—and Excel Services 2007—Sept. 24. The team explained the issue this way: Of the countless different floating point numbers Excel 2007 can store, there are six floating numbers using binary representation that cause the problem. Apparently for calculations that amount to around 65,535, Excel 2007 would return a value of 100,000 instead of 65,535.

As of Sept. 25, Microsoft reported that it had come up with a fix for the issue. "We take calculation in Excel very seriously and we do everything we can in order to ensure that calculation is correct for all cases," Gainer wrote. "Weve come up with a fix for this issue and are in the final phases of a broad test pass in order to ensure that the fix works and doesnt introduce any additional issues—especially any other calculation issues."

Before being broadly implemented, the fix needs to make its way through Microsofts build lab and onto a download site. "We expect this to happen very soon," he wrote. "Well add another post once thats taken place with a link to the download."

Click here to read more about Microsoft Offices pull.

In response to users comments that Microsofts explanation of the Excel issues was vague, Gainer said Sept. 26 that in trying to "walk the line between not too much detail and too much detail," his explanation might not have been clear.

"This is an issue in a function that puts numbers in cells, so the values in Excels memory are actually correct," he wrote. "Excel actually calculates the correct answer, … [b]ut in the function that takes that value and formats it to be displayed on the screen … there is a bug. Any calculations based off that cell will be accurate too."

One blog commenter mentioned that the issue can also be found in Visual Studio 2005. Microsoft has not confirmed any issues there.

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