A Fluorescence Activated Cell Sorting (FACS) instrument can distinguish and quantify different populations in a cell sample. In analytical mode, the output is a one- or multi-dimensional distribution of cells versus user specified properties. FACS can also be used to sort the cells according to user-specified cut-off values. It is most common to monitor the fluorescence intensity at one or multiple wavelengths. Single cell reading is achieved by passing the sample in a narrow flow through the detection chamber, and sorting occurs directly after detection.