Anemometers fall into two groups: those that only measure air or wind speed, and those that also measure airflow volume. The former group can be divided further into wind speed meters designed for outdoor use by outdoor sportsmen, and air flow meters used by manufacturing and HVAC technicians to measure the output of a fan. Airflow volume meters can calculate the exact amount of air provided by that fan by multiplying the measured speed of the air by the area of the grille or register through which it flows.