Im am writing the scientific report where I have a calibration curve. I want
to use that and find the concentration of an unknown sample. This is easily
done by hand, but how do i show it on exel and on the chart itself?

To extrapolate and find/show values on a calibration curve in Excel, you can follow these steps:

1. Enter your calibration data into Excel. This should include the known concentrations and their corresponding measurements.
2. Create a scatter plot of your calibration data. To do this, select your data and go to the "Insert" tab. Click on "Scatter" and choose the type of scatter plot you want to create.
3. Add a trendline to your scatter plot. Right-click on one of the data points and select "Add Trendline." Choose the type of trendline you want to use (linear, polynomial, etc.) and make sure the "Display Equation on Chart" and "Display R-squared Value on Chart" boxes are checked.
4. Use the equation of the trendline to calculate the concentration of your unknown sample. Simply plug in the measurement of your unknown sample into the equation and solve for the concentration.
5. Show the calculated concentration on your chart. To do this, add a data point to your scatter plot at the concentration of your unknown sample and label it with the calculated concentration.
6. Add a vertical line to your chart to show the measurement of your unknown sample. To do this, go to the "Insert" tab and click on "Shapes." Choose the line shape and draw a vertical line at the measurement of your unknown sample.

By following these steps, you can easily extrapolate and find/show values on a calibration curve in Excel and display them on your chart.

I will assume that the calibration curve is linear (y = mx + b)
In some cell (say D1) we can find the slope (m) with the formula
=SLOPE(y-values, x-values)
Something like =SLOPE(B2:B12, A2:A12)
Likewise in say D2 we can find intercept (b) with =INTERCEPT(y-values,
x-values)

Let D3 contain the measured y-value from which you need to compute its
x-value
Let these values be Y and X
So Y =mX + b or X = (Y-b)/m
Turning this into Excel: in cell D4 enter =(D3-D2)/D1

Now having done that, you need to be able to report also your confidence
intervals
See
http://people.stfx.ca/bliengme/Excel...onfidence3.htm

By the way: I hope you are INTERPOLATING for the calibration curve not
EXTRAPOLATING
The former is generally valid, while the later is fraught with dangers

best wishes
--
Bernard V Liengme
Microsoft Excel MVP
http://people.stfx.ca/bliengme
remove caps from email

"Heekla" wrote in message
...
Im am writing the scientific report where I have a calibration curve. I
want
to use that and find the concentration of an unknown sample. This is
easily
done by hand, but how do i show it on exel and on the chart itself?

Hi,
Following on from Bernard, once you've found the x and y values for your
sample, just plot them as a new series on the chart. You can also add x and
y error bars linking the point with each axis if you want to do it like in
the "old days" when we used graph paper.
Obviously, it looks better if you've removed the lines between the data
points and added a suitably formatted (preferably linear)trendline to the
chart. If you've done the calculations properly, you should see your new
sample point sitting on the trendline.
Don't be tempted to apply some higher order polynomial trendline just
because it looks to fit the data better.

Dave

url:http://www.ureader.com/msg/10297359.aspx