The Handheld XRF instrument is a remarkably stable instrument. Table 1 shows gives the average weight percent oxide for each major element calculated on only sawed surfaces from each of the five standards on each of the five data collection dates (July 2010, November/December 2010, June 2011, July 2012, and October 2012). When we compared these values both to one another and to the laboratory-reported values, we demonstrated the ability of the hXRF to provide data consistent with laboratory-reported values.