To use the LINEST function for the coefficients of a log trendline see
Trendline coefficients
http://www.tushar-mehta.com/excel/ti...efficients.htm

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Tushar Mehta
www.tushar-mehta.com
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In article ,
says...
I have been using the trendline - logarithmic type - on some charts. Although
the equation in the form
y = a*ln(x) + b
can be made visible on the chart, I need a function that will return the a
and b coefficients.

I can't find such a function. I don't think logest is the same.

Art