not be of any practical assistance, and plan to be self-sufficient. Other divers refuse to dive with anyone who is not trained to the same system. Many divers simply accept the status quo and do not even question the safety implications. Use of checklists Studies have shown that the use of written checklists can significantly reduce the number of critical human errors in occupations and procedures where a small number of critical checks can make a proportionately large effect on the risk of the operation. These are reminders to make critical checks for people who are well aware of the need, and highly skilled and responsible posts such as airline cockpit crew and operating theatre staff, who nevertheless occasionally fail to complete the necessary preparations in the absence of a checklist. The concept has been tested on a group of recreational divers and the reduction in undesirable incidents was highly significant. Checklist systems are more common in professional diving, where the code of practice or operations manual may mandate recording that each checklist has been applied. The checklist is effective when all critical checks are listed. Additional detail may be counterproductive as distraction. More detailed checklists may be appropriate where equipment is set up and tested. The pre-dive check mnemonics advocated by diver training agencies are less reliable, as they rely on memory, vary considerably, using different terms to refer to the same or similar set of checks and the order of checks is highly variable and can cause divers trained by different agencies to become confused when diving together. In some cases the same initial has been reused in the same mnemonic for several groups of checks. A written checklist covering the safety-critical checks in a logical order avoids the distraction of trying to remember what the next item to be checked should be, and ensures that all the checks are covered, even if the checks are interrupted. There are several stages at which the use of a checklist is appropriate. These include during dive planning, risk assessment, equipment setup (particularly assembly and function testing of rebreathers), preparing the diver for the water, and in emergencies for which there is a planned response. A commonly used special case of a checklist in scuba diving is the decompression schedule for a planned dive profile, often carried by each diver in written format on a wrist slate or wet notebook. The