The SEM is an analytical tool that uses a focused beam of electrons to form magnified images. Under ideal conditions, the SEM is capable of producing images with a feature resolution at the nanometer level. In addition to image capabilities, a properly equipped SEM can provide information on the elemental composition of microscopic features. Information on the image and elemental characteristics of a sample are obtained through the interaction of the electron beam with the sample material, which produces various effects that can be monitored with suitable detectors. The resulting signals, which include secondary and backscattered electrons along with characteristic photoelectron X-rays, can be collected in synchronization with the position of the electron beam to provide detailed spatial and compositional information. A computer controlled SEM (CCSEM) can provide simultaneous measurement of individual particle size, shape (aspect ratio), and elemental composition by combining an SEM, an X-ray analyzer (EDS), and a digital scan generator under computer control [Schwoeble et al., 1988].Use of the computer to control the analysis permits relatively large numbers of individual particles to be analyzed (e.g., 1000 s). Elemental composition, though an important benefit for research purposes,was not part of the round robin tests. Errors typically arise because of poor counting statistics for large particles, an inability to differentiate between primary particles and agglomerates, 3-D/2-D effects, and/or artifacts created during sample preparation.