Los Alamos National Lab, New Mexico. Research in the flow cytometry lab - sorting chromosomes for DNA Library. The counting of cells is called cytometry. Flow cytometry characterizes single cells as they pass at high speed through a laser beam. Speeds of up to 50,000 cells a second can be measured. The scattering of the laser beam provides a way to identify the cells. Many other characteristics, such as shape and surface texture can also be measured. The cells are then sorted as electrically charged droplets. This also purifies the samples. (1989).Human Genome Project.