Hand held (assuming that is what your friend had access to) XRF units are completely worthless for our needs. They do not read lighter elements, like Si or Al and above; so no carbon. Everything else that they do read are not overly accurate. They are good for determining the difference between 41XX and mild, for example, in the scrap yard or machine shop. Optical Emission Spectrometry (OES) gives much more accurate and precise readings for any element that the machine is set-up and calibrated for. For example, in these alloys I would be able to tell you the carbon to the first decimal point for certain, but the second would have a bit of variance since we do not make these alloys and thus don't calibrate them. With something like 1025, or 4330 that would move out one more decimal. Other things like Mn, Si, Cr, Ni, V, and Mo would be pretty good at 2 decimal places, and P and S get out to 3.