The present application is directed to apparatus and methods for determining a magnitude of defocus and a direction of defocus for a photolithography process. The chamber walls are advantageously formed of high-purity silicon as are other parts contacting the unground pellets or ground powder. A measuring device is provided with the depth gauge for measuring the relative distance between the tip and the reference member, and the measuring device has a large, digital display for providing the relative distance. The stored conversation attributes are updated in response changes in the conversation attributes caused by the one or more transaction messages. Layered structures for exit electrodes and deflector plates confine secondary ions in a local low-energy well, preventing them from entering the detector.