How the role of my second computer changes between recreational and technical dives.
How the role of my second computer changes between recreational and technical dives. Dive computers are useful only when the diver understands what role each one has in the plan.
What I want from the display
On frequent recreational diving I like two independent computers because I want continuity in decompression history if one device stops working. In technical diving the roles become more explicit: the Perdix 2 is my primary computer and the Mares Quad can be used in gauge mode as a time/depth reference alongside a separately prepared backup plan.
The key is that a backup is only useful if the diver knows what they will do when the primary device disappears. Two screens do not automatically create a strategy.
The practical point
The screen is useful, but the real safety feature is still the diver who understands the information and has a plan for losing it.
Two computers do not always have the same job
On recreational dives I want two independently running computers because I dive frequently and I want each instrument to maintain its own history rather than borrowing assumptions from the other. If one display fails, the other is still a computer that has been on my wrist for the same dives.
For planned technical decompression I use a different architecture: the Perdix 2 is primary, while the Quad can become a depth/time instrument in gauge mode and written backup information provides an independent plan. The point is not “always wear two computers.” It is to define what the second device is supposed to do if the first one stops.
A computer gives information; the diver still makes decisions
I like powerful dive computers, but I do not want them to become black boxes. Terms such as no-decompression limit (NDL), TTS, GF99 and SurfGF should mean something to the diver. My Perdix 2 uses Bühlmann ZHL-16C with configurable gradient factors in the modes I use, but a configurable algorithm is useful only if I understand what I am changing and why.
NDL and Time To Surface are predictive outputs. They are calculated from the computer’s model, current profile and assumptions; they are not promises about biology. TTS can include predicted ascent and required decompression based on enabled gases and the programmed ascent behaviour. This is why I use the screen as a decision tool rather than an authority detached from the dive plan.
Air integration adds context, not permission
With transmitters, pressure can be related to recent consumption and depth. Shearwater can calculate SAC and Gas Time Remaining, and its current sidemount support can track multiple cylinders and provide switch prompts. GTR is useful but it does not replace technical gas planning: Shearwater’s own documentation explains that it is based on a direct ascent with reserve assumptions, does not include safety or decompression stops, and is unavailable once required decompression is present. That is exactly why I describe it as additional information.
Redundancy changes with the type of dive
On recreational dives I normally let two computers run independently because I dive frequently and want both to carry their own tissue/loading history. On technical dives the Perdix 2 is the primary decompression computer and the Mares Quad can be used in gauge mode together with written backup tables/wetnotes. Those are different redundancy strategies because the dives are different.
What I want the diver to understand before the display
A beautiful screen is useful only if the diver knows what the numbers are telling them. I want to know which algorithm is running, which gases are enabled, what reserve assumptions affect gas calculations, how ascent-rate warnings work and what happens if the computer is lost. That understanding is what turns an expensive instrument into a tool rather than a source of false confidence.
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