FBRM (Focused Beam Reflectance Measurement) is a measurement technique used for in-process particle measurement. The precise and sensitive chord length distributions (CLD) are highly responsive to changes in size, shape, or count.  The probe is placed at an angle straight into process streams to allow particles to flow freely across the probe window where the measurement takes place. Through a system of optics, a laser beam is sent down the probe tube and narrowly focused on the sapphire window. The optics rotate at a constant rate (usually 2 m/s), which causes the beam spot to sweep through particles quickly as they pass by the window. Individual particles or particle structures will backscatter the laser light to the detector when the concentrated beam travels through the particle system. These separate backscattered light pulses are identified, counted, and the distance across each particle is determined by multiplying the duration of each pulse by the scan speed. The chord length, a crucial indicator of the particle's relationship to particle size, is used to determine this distance. Thousands of particles are typically counted and measured per second, enabling the real-time reporting of an accurate and very sensitive chord length distribution. The chord length distribution charts the evolution of particle size and counts from the start to the finish of a procedure. It is possible to chart the evolution of statistics from each chord length distribution, such as counts in the fine and coarse size classes.