A Portacount is a portable device used to measure the fit of respiratory protective equipment, such as masks, ensuring they provide adequate protection against airborne contaminants. It operates by comparing the concentration of a test aerosol inside the mask to the concentration outside, thereby calculating a fit factor. This device is widely used in occupational health and safety settings to ensure compliance with regulations and to enhance worker safety. It is particularly valuable in industries where workers are exposed to hazardous substances.