Good afternoon,

Thanks for the platform to address X-ray related questions. 

I was using XRFMap_Viewer in the Larch package to look at some uXRF data of my soil samples, and the main element of interest is Fe, and to some extent Mn too. I went through the steps to choose them (Ar was auto detected), calculate model, then fit model. Under the Composition tab, concentrations were given as in the screenshot below. The dropdown units has 3 options (ng/mm^2, wt % and ppm), but when i switch among them, none of the values changed. From a bit research online, I seem to understand there are two approaches to get absolute elemental concentrations. One is by measuring reference standards and establishing calibration curves, and the other is by fundamental parameters which is built-in in Larch (or XRFMap_Viewer in my case?). We didn't run any standards at the time. Could anyone please shed some light on how [Fe] in weight % can be computed in a built-in manner? Thank you.