Excel - FWHM Through Linear Interpolation

Part of the Advanced Excel training series which covers how to create a template to find the full width half max (FWHM) for a well behaved graph (one that does not have local minima/maxima near the rising/falling edge of the FWHM). The FWHM is calculated by linear interpolation utilizing both the point-slope formula and the slope formula, so this is expecting a data set of rather fairly closely spaced values; this only looks at the 1 data point to the left and the 1 data point to the right of the FWHM and calculates the x value. The video also covers how to overlay a FWHM bar on top of the data set.

[@b1961-e1d]

Thanks very much that was so useful to me

[@katesss]

Thanks for creating the video! It really helps!

[@Vera19910509]

Thank you for this video!!! :))

[@heloisamoreiramartins2179]

It's really helpful! Could you please share this example sheet?

[@beatrizairajacob93]

Thank you!! :D

[@mauroagt]

excelent!!

[@marinagarciaguijarro7818]

I DON'T UNDERSTAND ANYTHING

[@anthonyteran5346]

How would the excel formulas change for the case of a function that is not well behaved? Say for example your function dipped down to 40% in the center of the graph therefore there would be two flat peaks and 4 points where it would be at 50%. How would you calculate the FWHM for each of those peaks as well as the FWHM of the first 50% point and the last 50% point?

[@x68507]

If you had curve that had a central dip, the technique would still give you all the data points needed to calculate the intermediate FWHM and complete FWHM in Column M. However, to automatically determine the intermediate FWHM of each individual peak, you would have to use a different formula in P2/P3. The simple MIN/MAX used in P2/P3 will find the complete FWHM so you would need to use a more complex formula.
The easiest way to accomplish this would be to use Column J as a "helper" column that will count the occurrence of a value flipping across the FWHM threshold. You could use the formula '=COUNTIF($M$2:M2,">0")' in cell J2 and copy & paste it all the way down to cell J277. Then, use a simple VLOOKUP to find each of the "flips": =VLOOKUP(1,$J$2:$M$277,4,FALSE) where 1 will be the occurrence of the flip (you will need to know beforehand how many flips you're looking for), J will be your helper column, and M will be your FWHM column.
The following link is a markup of what you could do in this situation:
drive.google.com/file/d/0B2nEQjKE2EhxYTQtX1VOQ0hReHM/view?usp=sharing

[@anthonyteran5346]

Thank you Michael, I think the markup explains it all. I used your "Excel - FWHM Through Linear Interpolation" tutorial to create a spreadsheet almost exactly as yours but I have data that is not "well behaved." I will try your suggestions and thank you so much for the markup.

[@yahakoror5]

hello, how do you type something like"$Q$2" in the fx line?

[@x68507]

If you have the cell reference already in the fx line by either clicking the cell or using the arrow keys, you can press the F4 key at the top of your keyboard, you toggle between "Q2" then "$Q$2" then "Q$2" then "$Q2" and back to "Q2". This will change either the column (Q) or the row (2) from relative to absolute positioning.