I did not suggest that your data was not curved. I suggested that over an
appropriate range log(OD) might straighten it into a line. Barring that, you
would probably get a better fit from a model that flattens out toward max and
min values (as OD must) instead of increasing or decreasing without bound (as
a polynomial must).

Jerry

"PAUL GRAZIDE" wrote:

Polynomial in this case is correct, because the curve is not linear. If
curve was linear, then i would use y=mx+b.

Thanks


"Jerry W. Lewis" wrote in message
...
Are you sure that a polynomial is an appropriate calibration curve here?
You
don't give enough points to assess the fit, but I am much more familiar
with
OD calibration curves that are either log-linear or a 4- or 5-parameter
logistic equation.

Jerry

"PAUL GRAZIDE" wrote:

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.