How do I determine a y value for x ?

[Flyrodder]

I create a chart from data. I now want to use that chart and data to predict
the y value for any given value of x. How do I go about doing that in Excel?
Is there a way to do curve fitting to get an equation for a curve? HOw do I
go about doing any and/or all of this?

 

[Jon Peltier]

You can add a trendline to a chart series. You can use the trendline formula
(be sure to use enough significant figures to get a reasonable result) or
the LINEST worksheet function to get coefficients to compute Y values for
known X values.

- Jon

 

[Bernard Liengme]

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/ExcelTips/RegressionAnalysisConfidence3.htm