Dive Computer Conservatism Settings by Brand, With No-Stop Times

What does a conservative factor mean on a dive computer?

It means a setting that makes the computer more cautious than its base model. A conservative factor, or conservatism setting, adds margin to the decompression calculation, so the computer ends your no-stop time sooner and, on a decompression dive, asks for longer stops. Garmin's Descent manual says it in one line: higher conservatism gives a shorter bottom time and a longer ascent time. For a course quiz, the short answer is that it adds a safety margin by making the no-decompression limits shorter.

The setting sits on top of the model; it does not replace it. How Bühlmann, RGBM and gradient factors work is covered in dive computer algorithms explained, so this guide stays with the menus. Each brand adds its margin a different way. Some lower the gradient factors, older Oceanic computers cut the limits to those for the next higher 915 m (3,000 ft) of altitude, and Scubapro adds extra stops.

Aqua Lung uses the exact phrase. The i330R has a Conservative Factor with three settings, OFF, MORE and MOST, and each one is a preset pair of gradient factors. Suunto describes the trade from both sides: for a recreational diver, conservative means less time in the water to avoid decompression, while for a technical diver it means more time in the water because the decompression gets longer.

Conservatism settings by brand: names, ranges and defaults

Every row comes from the maker's own manual or support page. Where the document does not print a value, the table says so instead of guessing.

Two notes. Garmin's Descent Mk3 and G1 manuals describe conservatism levels and a Custom gradient factor option but do not print the preset values. The CMAS fact sheet on gradient factors lists them as 45/95, 40/85 and 35/75, the same as Shearwater's. The same fact sheet gives the Suunto Ocean default as 45/80, while Suunto's own page says 40/85, so check secondary lists against the manual. Defaults also differ inside one brand: the Suunto Ocean starts at 40/85, but the EON Core in Bühlmann mode starts at 30/70 and shows any other value in red.

How many no-stop minutes each setting costs

One preset step changes the no-stop time at 18 m on air by about 10 minutes. We ran our scuba deco planner, which uses Bühlmann ZHL-16C with gradient factors, for each GF High in the brand table. The descent at 18 m/min counts as bottom time. A brand's own code, and its RGBM or MB-level options, will give different numbers, so read the table as the size of each step, not as what your screen will show. For what an NDL is and how tables set it, see no-decompression limits explained.

Only GF High matters on a no-stop dive. Shearwater's manual defines GF High as the supersaturation allowed when you surface, and a no-stop dive is one where you can surface directly, so GF Low never comes into play. In our planner 35/85, 40/85 and 85/85 all give 47 minutes at 18 m. That is why the Mares Genius default (85/85) and the Shearwater default (40/85) start a recreational dive with the same no-stop time in this model, though they would place decompression stops differently. CMAS makes the same point: no-stop limits depend only on the surfacing M-values.

In percentage terms the steps are large. At 18 m on air, going from Med (GF High 85) to High (75) removes 10 of 47 minutes, about 21%. Dropping to 70, the Suunto EON Core default and Aqua Lung's MOST, removes 14 minutes, about 30%. At 30 m the gap between the Low and High presets is 7 minutes on a limit that is only 12-19 minutes long.

When to choose a more conservative setting

Choose one when something about you or the dive adds risk that the model cannot see. Suunto's scale is the most concrete: 0 for ideal conditions, +1 when some risk factors exist, +2 when several do. These are the factors the makers and DAN name:

On a gradient factor computer, one step usually means moving from the default to the High preset, 40/85 to 35/75 on Shearwater and the Suunto Ocean. Mares builds the steps into the Genius instead: PHYSIO lowers both gradient factors by 10 per step for how you feel about yourself and diving overall, I TODAY by 5 for how you feel that day, and DIVE by 3 for the conditions. For the evidence behind each factor, see why divers get DCS within the limits.

• Cold water. Suunto names water colder than 20 °C (68 °F). Mares suggests its DIVE adjustment when you expect strong current or very cold water.
• Hard work. Suunto lists strenuous activity during the dive and exercise before or after it, and the Mares Puck Pro manual names a strenuous dive as a reason for its P factor.
• Age. Suunto says particularly over 50. DAN's Neal Pollock puts it as aging making us all less bulletproof than we once were.
• A long break. The Puck Pro manual gives a long period of inactivity as a reason for extra margin.
• Fatigue, dehydration, stress, tight equipment and obesity, all on Suunto's list. Its fatigue item includes lack of sleep and exhausting travel.
• A patent foramen ovale (PFO), the opening between the upper chambers of the heart. Suunto lists it among the factors for both its RGBM and Bühlmann computers.
• Many days of repetitive diving. DAN's Nick Bird sees staying close to NDLs across a dive series as a likely contributor to many DCS cases. Cressi's manual tells divers not to exceed two dives a day and to leave at least 2 hours between dives.
• After a mistake. Shearwater's manual tells you to use extra conservatism for later repetitive dives after a missed stop or an ascent faster than 10 m/min (33 ft/min).

Should you change settings in the middle of a dive trip?

Pick the setting before the trip, and once it starts, only move toward more conservative. A setting changes the limit, not the nitrogen your computer has already counted from earlier dives.

Some makers restrict changes between dives. Suunto says changing the algorithm between dives is not recommended while the no-fly time is counting down, and Oceanic's BUD locks its algorithm choice, DSAT or Z+, for 24 hours after a dive. Mares goes the other way and adds margin as a trip goes on. With MULTIDAY switched on, the Genius lowers both gradient factors by 2 on the second day of diving, 2 more on the third and 2 more on the fourth, to a maximum of 6. Its manual explains why: the effect of inert gas building up over several days is not fully understood and differs between people. Its REP DIVE option cuts both values by 8 when you surface and restores them over a two-hour surface interval.

Changing to a more conservative value during a dive is a different case. Pollock notes that a computer allowing changes underwater lets you lower GF High after working harder at the bottom than planned, and Mares lets you change the Genius DIVE setting underwater because conditions can turn out different from what you expected. Scubapro works in reverse if you skip its extra stops: ignore a level stop on L8 and the G2 drops you to L7 or lower, so the margin you chose is only there if you follow it.

Check the setting before every dive. Suunto's pre-dive checklist puts the altitude setting and the personal setting alongside the display, battery and gauge checks.

Diving with a buddy whose computer uses different settings

Agree on one plan and end the no-stop phase when the more conservative computer says so. Nick Bird puts the problem plainly in DAN's Alert Diver: unless divers use the same computer with the same breathing gas and safety settings, each gets different NDLs throughout the dive. DAN's guide to dive computers sees a real benefit in diving with people whose computers use a similar model and settings, and says following the most conservative directive will likely not be a burden for the group.

Our planner shows how far apart two settings get. Take a 15-minute dive to 30 m on air, descent included. At 40/85 or 45/95 it is a no-stop dive. At 30/70 the same profile needs 4 minutes of stops: 1 minute at 9 m, 1 at 6 m and 2 at 3 m. One buddy finishes with a safety stop while the other is on a decompression schedule. Scubapro's G2 manual describes the same split between an L0 and an L9 unit: the L9 diver gets a shorter no-stop time and extra level stops.

Garmin lets two Descent owners copy settings across. Setup Sharing transfers dive settings to another diver's computer, such as an instructor's, and when two units' tissue loads disagree after a transfer, Garmin's troubleshooting notes name a different high gradient factor as one cause and tell you to match the settings. On other brands, open both menus side by side before the dive.

Which setting should you start with?

The factory default, until training teaches you to change it. The makers warn against going further without that: Shearwater says not to edit GF values until you understand the effects, Garmin asks you to understand gradient factors before entering a custom level, and Suunto's personal setting page warns that 0, -1 or -2 carry a high risk of DCS. Mares asks for a code before it allows the ADVANCED setting that raises the Genius to 90/90, and says it does not recommend it.

From there, add steps for the factors above. Cold water below 20 °C, fatigue from an overnight flight and an age over 50 are three items on Suunto's list, which fits its description of +2: several risk factors. A conservative setting still does not make a dive safe. DAN notes that divers do develop DCS after dives inside their computer's limits, because models predict outcomes and do not guarantee them.