Excel addition problems - Microsoft's response

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Here’s Microsoft’s response to the anomalies found in Excel’s adding up.

We asked Microsoft for a comment on the Excel addition problems that our readers have been discovered. Office Watch pointed out the anomalies in results when the same numbers are added in a different order or grouped differently – something that should make no difference to the result.

The company response was:

This behavior is not a bug in Excel. Excel was designed in accordance to the IEEE Standard for Binary Floating-Point Arithmetic (IEEE 754). The standard defines how floating-point numbers are stored and calculated, and requires that numbers be stored in binary format. The IEEE 754 standard is widely used because by specifying numbers be stored in binary format it reduces storage requirements and allows the built-in binary arithmetic instructions that are available on all microprocessors to process the data in a relatively rapid fashion.

For more information on Excel’s use of the IEEE 754 standard and workarounds available, please see KB article 214118, “How to correct rounding errors in floating-point arithmetic”.

To some of our readers that will seem like a reasonable response, to others (the ‘arithmetic is arithmetic’ camp) it will sound like a brush off.

The IEEE 754 standard that Microsoft uses to justify the maths errors in Excel is a long and complicated document – Wikipedia has a good summary.

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