Human: I'd like to know about the different types of scuba diving gear. Assistant: 
Scuba diving equipment is typically divided into two categories - open circuit and closed circuit. Open circuit refers to a system in which air from the surface is fed directly into the diver's helmet, while closed circuit systems use a tank of compressed gas that is carried by the diver and used to power their dive equipment. The main differences between these systems are the amount of control over depth and duration of the dive, as well as the level of safety they provide. Open circuit systems tend to be more affordable and less complicated, but may not offer as much control or safety as closed circuit systems.