Introductory diving  Introductory diving, also known as introductory scuba experience, trial diving and resort diving are dives where people without diver training or certification can experience scuba diving under the guidance of a recreational diving instructor. Introductory diving is an opportunity for interested people to find out by practical experience if they would be interested in greater involvement in scuba diving. For scuba instructors and diving schools is it an opportunity to acquire new customers. An introductory diving experience is much less time-consuming and costly than the completion of autonomous diver training, but has little lasting value, as it is an experience program only, for which no certification is issued. Introductory scuba diving experiences are intended to introduce people to recreational diving, and increase the potential client base of dive shops to include people who do not have the time or inclination to complete an entry level certification program. Participants are usually required to read and sign waivers to minimise liability of the program provider, and to provide a declaration that they do not suffer from any medical condition listed that would be an unacceptable risk for diving. Prior to the dive itself, an instructor teaches essential theoretical knowledge, so that the participants can dive with a low level of risk, and with informed consent. After putting on the necessary diving equipment, the participant enters the water under close supervision of the instructor. First of all, breathing from the scuba regulator is practiced at the water surface. At shallow water depth, some scuba skills are learned: Clearing the diving mask, removing the regulator from the mouth and replacing and clearing it of water. These two skills are essential for the safety of the participants. Afterwards, there may be an opportunity to either play underwater games or explore the surroundings in shallow water. Trial diving usually takes about two to four hours. The participant learns the basic minimum safety guidelines and skills needed to dive under the direct supervision of a diving professional. If an open water dive is included, a few more basic skills will be practiced in confined water. The course includes:  Usually the introductory diving first takes place in "confined water", which usually means a swimming pool or a very shallow and safe place in a lake or the sea. Depending on the offer, after the first dive in confined water, a second or further shallow dives may be done in suitable confined or open water. People can go directly from high altitude to scuba diving, but should not scuba dive then go up in altitude without allowing an interval, depending on the time and depth of the dive, to reduce risk of decompression sickness.