I think R-squared has already been defined. It is a single number.
Perhaps you could restate your question. Do you mean you want to calculate
the R-squared value for a second order polynomical fit to the data?

Look at the LINEST function.

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Regards,
Tom Ogilvy

"Metin" wrote in message
...
I want to calculate the R-squared value on chart with an Excel formula.
But the R-squared value has to be a 2nd order polynomial.