is long enough to forget some skills and knowledge, so a refresher may be required. It is preferable to do both parts within a short period, and this may be logistically complicated, and the weather conditions may not be conducive to this schedule. The change between instructors may not be helpful, as they may differ in style and personality, and there may be small differences in technique which could cause confusion, but could also provide a better range of experience. It is also likely that rented equipment will be unfamiliar at the referral site. An unfamiliar set of equipment should be tested in benign conditions where adjustments can be made in comfort and safety, which requires more time. There may also be an increased cost because of the split between two service providers, the additional paperwork and other overheads and sometimes the necessity to repeat training of forgotten skills. References Underwater diver training