If you have GX and SD you must use filings, almost like dust. It will read DNA not just nail. You can do biofeedback with a nail if you are using the pulse and the XM generator, but as said above, it is not as effective with the GX. Turning it into a powder is referring to the digitizer which is with the GX, not the XM. The best option for biofeedback with the GX is contact. Taking into consideration what your issues are. For example, if I have a cold, I put sputum in the SD. I get amazing and quick results. Some use urine for kidney issues or bladder infection. Hope that gives you more direction.
For more details, please check the link: