Put the Conc data in column A and the OD data in B
You can have headers ("Concentration", "OD" ) in row 1
Let's say the last row is 10
Select A1:B10, click the chart tool, select XY chart, use the first subtype
(markers without line)
On chart right click on a data point, select Insert Trendline and specify
polynomial or required order
To out the coefficients into cell use LINEST as shown in
http://www.stfx.ca/people/bliengme/E...Polynomial.htm

You now have equation such as y = ax^2 + bx +c where x is conc and y is OD
You will have real numbers 12.45 = 2.34c^2 - 5.46c + 8.9 and will need to
solve for x

Most calibration curve I every used were linear y =mx + b
So x = (y - b)/m

best wishes
--
Bernard V Liengme
www.stfx.ca/people/bliengme
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"PAUL GRAZIDE" wrote in message
...
I am setting up a chemistry calibration curve using data below

OD reading Concentration
.020 0
.045 10
.245 40 etc

Plotting in XY scatter chart and get trendline using polynomial function.
How can I determine the concentration of an unkown solution ? I want to
use trendline data to do this.