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65,536 Lashes for Microsoft

Posted by: Stephen Wildstrom on October 1, 2007

Microsoft should be more abashed than it seems to be about a bug in Excel 2007 that causes certain multiplications that produce results very close to 65,535 or 65,536 to display incorrect answers. For example, if you multiply 850x77.1[see note below], the result is displayed as 100,000. The correct answer, 65,335, is stored and that’s what is used in most, but not all, operations when the cell is referenced.

In a post to the official Excel blog on the Microsoft Developers’ Network, David Gainer points out that the error only affects 12 specific values out of a total of more than a billion billion possible floating point numbers. I’ll have to take that on Microsoft’s word, but it’s really beside the point. Even one math error on a program counted on as much as Excel is won’t do. And it’s especially bad when it crops up in a new version of a program that has been around for as long as Excel has.

Gainer says that developers have come up with a preliminary fix that is now undergoing testing. They plan to test it thoroughly before releasing a patch, a very good idea because it is very easy for such repairs to cause new and unpredictable problems.

At least Microsoft is better off than Intel was when floating-point division errors turned up in the then-new Pentium processor. It had to recall and replace the bad chips, an expensive proposition. Microsoft can fix the damage, if not the embarrassment, through the all-too-common process of downloading a software patch.

NOTE: This was originally published as 805x77.1, an expression that gets the right answer in Excel but the wrong one in my post. Sorry for the fumble fingers--and even blogs need editors.

Reader Comments


October 1, 2007 7:25 PM

Hey My excell Mac comes up with:

805x77.1 = 62065.5

65335 is also wrong???

Bad slide rule?

Dust off your calculator?



October 2, 2007 1:53 AM

It's actually 850x77.7 - 805 is a typo.



October 2, 2007 1:56 AM

Vista here, same result... 62065.5

I'm confused...

John Squires

October 2, 2007 2:06 AM

It's just a typo - he meant 850 * 77.1.


October 2, 2007 3:14 AM

805 x 77.1 = 62065.5
I guess you guys were using excel to get the correct answer, 65,335 :)


October 2, 2007 3:20 AM

Clearly a pismrint for 850x77.1.
Also 65335 is a tpyo for 65535. Really, it is very easy to make misteaks when your typing fest.


October 2, 2007 4:52 AM

62065.5 is correct. I guess my calculator is dusty too.



October 2, 2007 5:32 AM

It's just a typo. He's put 805 instead of 850. He also mistakenly put the number as 65335 at the end of the first paragraph. The correct numbers are 850 * 77.1 = 65535.


October 2, 2007 7:28 AM

Obviously suffers from "Numerographic dyslexia". Should say 850*77.1

Chris P.

October 2, 2007 7:53 AM

Ummm, my calculator tells me 62065.5. Way 2 go.


October 2, 2007 9:41 AM

I pay as much attention to Stephens' articles as I do to my IT
courses classes. Tough I think the simple problem with Excel lies with a not so user-friendly Interface, the real big problem is that you are bound to typing errors for long rows, especially if you want to look at the same data from a different angle. Take sales data. if you want a look at geo locations and/or quartiles you have to copy & paste all the data into different cells. In Excel data is subjugated to document format. If you use a modeller, say Quantrix, you can play with data around without even needing to open a different document, or change tab pages. Content is completly free from form (at). For a better example of a spreadsheet Interface, my choice is the Thinkfree office suite.


October 2, 2007 10:45 AM

HAHA. This is hilarious! You post an article about how the Excel coders made a mistake yet you make an honest mistake in your own article?

Steve Wildstrom

October 2, 2007 2:59 PM

I confess, it's embarrassing making a mistake in a post criticizing someone else's mistake. I will say, though, that code should be subjected to somewhat more rigorous testing than our scribblings.

mm makes a good point about Excel abuse: Because it's ubiquitous and everyone sort of knows how to use it, Excel tends to get used in a lot of places where it shouldn't. For complicated models, there are specialized modeling tools. Engineers then to favor MathCAD. Mathematicians and financial analysts use powerhouse packages such as Mathematica, Maple, and Matlab. They aren't cheap and take some effort to learn, but they really do the job well.

Ben Franklin

October 2, 2007 4:34 PM

I just couldn't believe this until I tried. Microsoft needs to do better job testing before bring out a product.

AC Slater

October 4, 2007 5:06 AM



October 12, 2007 11:48 PM

it's possible to make up to 256 mistakes in each cell of the 256 columns by 256*256 rows of an excel spreadsheet. But lets count bytes for a bit. 256*256 = 65536 = 16 Bits....What is that Binary Number again?... oh yeah, [100000] (not to be confused with ten thousand)

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