an entry-level diver will normally learn include: Preparing and dressing in the diving suit Assembly and pre-dive testing of the scuba set. Entries and exits between the water and the shore or boat. Breathing from the demand valve Recovering and clearing the demand valve. Clearing water from the mask, and replacing a dislodged mask. Buoyancy control using weights and buoyancy compensator. Finning techniques, underwater mobility and manoeuvering. Making safe and controlled descents and ascents. Equalisation of the ears and other air spaces. Assisting another diver by providing air from one's own supply, or receiving air supplied by another diver. How to return to the surface without injury in the event of a breathing supply interruption. Use of emergency gas supply systems (professional divers). Diving hand signals used to communicate underwater. Professional divers will also learn other methods of communication. Dive management skills such as monitoring depth and time and the breathing gas supply. Buddy diving procedures, including response to buddy separation underwater. Basic dive planning regarding choice of entry and exit points, planned maximum depth and time to remain within no decompression limits. Limited recognition of hazards, emergency procedures, and medical evacuation may be included. How to adapt when facing strong current The ability to remove and re-attach gear while underwater Can achieve neutral buoyancy Some knowledge of physiology and the physics of diving is considered necessary by most diver certification agencies, as the diving environment is alien and relatively hostile to humans. The physics and physiology knowledge required is fairly basic, and helps the diver to understand the effects of the diving environment so that informed acceptance of the associated risks is possible. The physics mostly relates to gases under pressure, buoyancy, heat loss, and light underwater. The physiology relates the physics to the effects on the human body, to provide a basic understanding of the causes and risks of barotrauma, decompression sickness, gas toxicity, hypothermia, drowning and sensory variations. More advanced training often involves first aid and rescue skills, skills related to specialised diving equipment, and underwater work skills. Recreational Recreational diver training is the process of developing knowledge and understanding of the basic principles, and the skills and procedures for the use of scuba equipment so that the diver is able to dive for recreational purposes with acceptable risk using the type of equipment and in similar conditions to those experienced during training. Recreational (including technical) scuba