An Okapi stands on a set of scales. Annual animals weigh-in and measure to record vital statistics at ZSL London Zoo. Every year the Zoological Society of London (ZSL) performs an animal weigh-in at London Zoo. The height and mass of every animal in the zoo, of which there are over 19,000, is recorded and submitted to the Zoological Information Management System. This is combined with animal measurement data collected from over 800 zoos and aquariums in almost 80 countries, from which zoologists can compare information on thousands of endangered species.