Cochran was one of the first companies to wet its fins in the multi-gas computer arena, and its long history in the tec community shows in a computer design tailor-made for deco-hounds.
Packaging The Gemini is really a two-computer system. The tank unit is a small black brick that measures cylinder pressure, depth and other factors and computes, stores and transmits all necessary dive data to the wrist unit to be displayed. The wrist unit is a slim 2.5-by-3-inch rectangle that offers an uncluttered display worthy of the most narcotic depths. It has its own sensors and can operate as a full-function dive computer on its own should the tank unit stop sending data. Unique among this group of computers, the Gemini uses three touch contacts instead of buttons for selecting modes and features.
Core functions The Gemini is something of a custom computer: The diver can order it in many configurations, compatible with air or with one, two or three blends of nitrox. As many computers do today, the Gemini automatically accounts for a wide range of environmental factors, such as water temperature, altitude (up to 15,000 feet), fresh or salt water and previous dive profiles. However, the computer also records environmental changes between dives and uses that information in its calculations. This is great for divers traveling to multiple destinations, as the computer tracks altitude changes while flying between diving days. Also, in dive-planning mode, dive times are calculated based on the use of all programmed mixes, not just the selected or primary mix. The diver can even choose a preprogrammed variable ascent rate (60 fpm under 60 feet, 30 fpm over 30 feet and the same rate as depth between 30 and 60 feet) or program in a custom fixed rate of ascent between 20 and 60 fpm. Also, a user-selectable conservatism function is expressed in a range of 0 to 50 percent When it comes to deco profiles, the Gemini will never lock up. If a diver violates a deco stop or surfaces early, the computer will continue to give off-gassing credit on the surface until the residual nitrogen is cleared. One of the Gemini's signature features is automatic gas switching. When the tank unit senses a stop in pressure drop from the main tank, the computer automatically switches to the second breathing mix. If the diver switches back to the main tank, the computer senses this too and follows suit. To switch to a third mix, the diver preprograms two parameters (time and depth) into the computer. Since the third mix is typically a high-oxygen deco mix, it is used at the end of a dive and in shallow water. When the diver passes the time mark and ascends to the preprogrammed depth, the computer automatically switches to the third deco mix. Divers have also long appreciated the fact that Cochran computers run on easy-to-find and easy-to-replace batteries. The tank unit swallows AAs of any flavor, and the wrist unit runs on N-size batteries.
Bonus What else can the Gemini do? Well, rebreather divers rejoice, because the Gemini supports not only three nitrox mixes, but also two constant PO2 blends. This makes the Gemini a great addition to a closed-circuit system, and it allows the diver to use more than one diving apparatus over one day or several days while easily keeping track of nitrogen and oxygen exposure levels.