The analyzing crystal must be oriented so that the crystal diffraction plane is directed in the appropriate direction. Figure 6.1 shows a simplified schematic of the WDS spectrometer. A scintillation or flow-proportional detector usually measures the fluoresced radiation. The heights of the resulting pulses are proportional to energy so using a pulse height analyzer (PHA), scattered or undesired diffraction-order x-rays can be rejected. The x-ray beam is usually collimated before and after the analyzing crystal.