Few quantitative analysis techniques attempt as large an extrapolation between the compositions of standards and samples than is attempted in electron microbeam x-ray emission analysis. In-situ x-ray microanalysis can be performed for essentially all elements in the periodic table in complex matricies that may contain, in extreme cases, thirty or more detectable elements. Analyses are attempted for the same elements, using the same standards, in various matrices whose average atomic numbers might range from 4 to 94. Unlike most analytical techniques, where suites of standards are synthesized having similar bulk compositions as the samples and bracketing the concentrations of the elements of interest, the standards employed in microbeam analysis are most commonly pure elements, simple oxides, or other binary element compounds. This is true even though matrix effects on electron retardation and scattering, x-ray absorption, and secondary x-ray fluorescence can cause major variations in the differences between relative intensity and relative concentration.