The variance function is more accurate for very high numbers in Excel 2003 than in Excel 2002.
Some functions will give different results in Excel 2003 compared to previous versions of Excel, because some behind-the-scenes work has gone on to improve various functions. A "two–pass" procedure is now used, which increases the accuracy of the results.
For a full list of functions that have been updated, see the Quick Reference Card. If you have worksheets in older versions of Excel that use any of these functions, you may want to recalculate your results in Excel 2003, as the new answers will be more accurate.