Wednesday, September 26, 2007

The bug in Excel

In all likelihood, Bill Gates must be using Excel spreadsheet to compute the value of his shares in Microsoft. In that case, he’d better recheck the math using- gee, the simple calculator.

Spreadsheet math has been one of those things most of us have taken for granted, but a bug newly uncovered in Microsoft's 2007 Excel program may bring some to reconsider.

According to the spreadsheet program: 77.1 x 850 = 100,000, way off from the correct answer of 65,535. Microsoft, in the final phases of testing a fix to the spreadsheet bug, says the problem occurs in only 12 very specific cases.

So how did a powerful program like Excel end up choking on a calculation that your everyday calculator can do? Says AppScout: "It all boils down to the fact that you can't represent an infinite group of non-integer numbers using a finite number of bits. In fact, Excel can store "only" about 9 quintillion distinct values. The numbers going into your calculations may be infinitesimally different from the number displayed, and for two calculations that nominally have the same answer the result may be infinitesimally different. Excel generally manages just fine in dealing with these tiny differences, but in exactly 12 instances out of the 9 quintillion possibilities it goes completely bonkers."

Wolfram offers a good, in-depth explanation of this issue, and why it's hard to get arithmetic right.

Especially in the age of energy efficiency and global warming, perhaps it's time for us to reconsider the abacus -- at least for the easy stuff.

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