View Single Post
  #3   Report Post  
Posted to microsoft.public.excel.charting
Bernard Liengme Bernard Liengme is offline
external usenet poster
 
Posts: 4,393
Default How can i extrapolate and find/show values on a calibration curve

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?