According to the Microsoft link
"... We sometimes get mails from our customers claiming to have found a calculation error in Excel, when in fact the calculation isn’t wrong, but the side effects of binary floating point precision make it seem that way. ..."
The article doesn't explain how the square root of a squared number can yield a negative number. Just a simple variance, always a positive value for archaeological counts and measures, nothing esoteric, yet taking the square root, there it was: a negative standard deviation. I quit using Excel (or any other spreadsheet for statistics after that). I still don't get quite how that number, which was seriously wrong, only "seemed" that way.
Biting the hand that feeds IT
