Microsoft Excel is the back of the envelope for the modern problem solver. If a problem can't be solved in a few cells and perhaps a pivot table, then perhaps it's a problem best left alone — or left for the mathematicians in any case.

As such, recent news of a calculation bug in Excel 2007 has caused quite a stir.

In a blog post, Microsoft employee David Gainer reported that there are occasions where, when the result of a multiplication should be 65535, Excel instead displays 100000 as the answer.

You can try this yourself. Multiply 77.1 by 850, 10.2 by 6425 and 20.4 by 3212.5.

"Further testing showed a similar phenomenon with 65,536 as well," Gainer blogged.

According to Gainer, Excel gets the calculation correct but does not display it. The bug is limited to six numbers from 65,534.99999999995 to 65,535, and six numbers from 65,535.99999999995 to 65,536.

Microsoft have released a hotfix for the problem that can be downloaded and it will be included in the the first service pack update of the program.

Dan B, a Microsoft employee, commented on the Microsoft blog that:

"We're not planning to share details on this beyond what we've already communicated — i.e. that the issue occurred in formatting of floating point numbers near 65,565 and 65,536. It was code that we introduced as part of the calculation overhaul that we did for Excel 2007 however."

The problem seems to be an error in the 64-bit floating-point to string conversion routine. You can read more about this on the Microsoft blog.