X-ray excitation conditions (beam electron intensity measured in terms of X-ray counts per second) are calibrated first, using a standard to ensure reproducible results. Before a run starts, the SEM column parameters (kV, spot size, etc) are automatically adjusted. After each sample stub is completed, the stage can relocate to the standard and perform a new calibration. Following X-ray count-rate adjustment, the background detector is calibrated in relation to Z (atomic number), using the calibration standard delivered with the system. The purpose of this is to search for particles based on the average Z, and not to rely on their video intensity as in most other systems. This is a key feature of the GSR software. Particles are detected based on their average atomic number falling within a user-defined Z-window. The SEM motorized stage is automatically driven to each standard, and the video levels are measured without changing any column conditions. The BSD response curve is then used to set upper and lower threshold criteria for particle detection by the BSD, based on the average atomic number. This serves as input for the preliminary search on particles in the automatic routine. The calibration process may be performed unattended during the course of a run in cases where the SEM gun is unstable.