This guide is intended to walk you through my recommendations for the configuration of your Shearwater Perdix for open circuit diving. You can choose to adjust settings as you see fit from these recommendations after class (this is not a set of GUE requirements). However, I would recommend only making adjustments only with experience and understanding.

Access the System Setup by pressing the left button on your Shearwater Perdix repeatedly until the System Setup option appears. Press the right button to enter the System Setup menu. Once in the System Setup menu, the right and left button’s actions are displayed next to the buttons in the lower right and left hand corners of the Perdix.

Mode should be set to OC Tec for all divers (recreational and technical). This mode is flexible enough to accommodate any kind of open circuit diving. By always using OC Tec you can avoid having to learn different computer layouts.

Salinity can be set to Salt, even when diving fresh water. My recommendation is to keep salinity set to salt for all your dives (regardless of if you’re diving in fresh, brackish, or salt water). This will not affect your decompression calculations as the computer calculates deco based on pressure, not distance from the surface. Keeping this setting on salt will will also keep the computer in sync with GUE’s Deco Planner, which uses salt water for all calculations. In addition, never changing salinity will keep you consistent with your teammates computers and avoid mismatches between salinity settings.

Conserv(GF) should be set to to 20/85. These are GUE’s standard gradient factors, and this will keep you consistent with GUE’s printed tables and decompression calculations in technical diving courses. We will discuss the choice of gradient factors in class, but we will be using 20/85 during all course dives.

Last Stop should be set to 10ft.

NDL Display should be set to @+5. The selection in this section will display in place of the NDL display once you have no additional NDL remaining. Recreational divers should never see this appear, but you will see it during technical dives. The @+5 display will show you how much deco you will have in 5 minutes if you remain at the current depth breathing the current gas. It’s a preview of your decompression obligation. We’ll talk about how to take advantage of the @+5 information in technical classes.

Clear Cntr can be set to Off. Clear cntr is an abbreviation for “clear counter”, which will show how much time has elapsed since decompression has cleared, if you encountered required decompression during a dive. This is not a particularly useful piece of information, so I disable it to avoid clutter.

AI stands for Air Integration (wireless transmission of tank pressure to the Perdix). Although using AI outside of class is not expressly forbidden, there are some major downsides we’ll discuss. In order to reinforce estimation skills we learn in class as well as to practice unclipping and reading the SPG, we won’t use AI.

AI Mode can be set to Off.

The Center Row screen controls what optional data appears on your screen during a dive. While many divers believe that more information is better (and Shearwater provides many options), I would recommend restraint.

Focus on displaying information that is useful. Blank space is not wasted space; instead, it focuses attention on the most useful information.

You will need AVG (the average depth of the dive) and Timer (a resettable stopwatch) displayed on the center row.

You may choose to enable additional information on the Center Row, if you understand it and if it is truly useful to you. The location of AVG and Timer is up to you, but the Perdix will only allow each in certain locations.

This screen is deceptively simple, and allows you to tell the computer which gasses you’re using during a dive. You can program in all the gasses you’re certified to dive. The example shown in the image above is for a GUE Tech 1 diver. You should not program any gasses into the computer you’re not certified to dive.

WARNING
It is critically important to understand what On and Off mean on this screen. Your ascent and decompression planning will assume the use of any gas marked On. Leaving gases set to On when you do not intend to use them can result in incorrect (and potentially dangerous) decompression calculations. Always verify that only the gases you plan to use during the dive are marked On, and that all others are switched Off.

The Alerts Setup screen configures the alerts for the computer. When triggered, alerts will appear during a dive and may vibrate your computer as well (provided vibration is available and enabled).

Alerts can be useful for less experienced divers, particularly when they always dive within strict limits. For example, an open water diver who only dives on air may consistently have the same depth limit on every dive. In contrast, GUE divers often operate with a wider range of limits that vary depending on equipment configuration, gases, and team objectives. Poorly configured alerts (those that appear but must be ignored during the dive) are distracting and worse than having no alerts at all. For this reason, I recommend disabling alerts unless you find them genuinely useful.

Depth should be set to Off

Time should be set to Off

Low NDL should be set to Off

Vibration should be set to Off

Depth Units can be set to your preference; however, a skilled diver should be able to use the units that are in common use locally. Teams using mixed unit systems put themselves at elevated risk due to difficulty in converting and communicating critical information.

Temp Units are purely for your reference, and should be set to your preference.

Brightness can be set to Auto, which will lower brightness when the environment is dim, and brighten the screen when it’s bright outside. This avoids a blindingly bright computer, and an illegibly dim one as well.

Altitude should be set to Auto, which will allow your computer to automatically adjust for altitude dives.

Flip Screen is used for divers who would like to wear their computer upside down. I recommend you do not flip your screen.

The digital compass can be configured on this screen.

Compass View sets the range of the compass dial that is visible on the main screen. You can adjust this setting as you see fit.

Calibrate initiates the calibration procedure, which should be completed whenever the battery is changed. I recommend recalibrating the computer prior to using it for important navigation on a dive.

True North can be used to allow your digital compass to point to True North rather than Magnetic North. Although this is helpful in theory, in practice it often leads to confusion as most compasses point to Magnetic North. As long as your navigation is based on relative directions, then this setting is not necessary and should be left at 0°.

Date should be set to the local date.

Clock should be set to the local time.

Unlock can be used to unlock additional paid features in your computer (for example, VPM or Avelo mode). You can ignore this option.

Log Rate controls how often your computer samples and records your dive. The default of 10 sec works well.

Reset to Defaults will reset your dive computer to defaults. It is not recommended to reset your computer to defaults.

The Advanced Config screen will allow you to configure additional options for your Perdix. For example, you can tell the computer what colors to use on the screen and what PPO2 is considered dangerous. Generally it’s best not to adjust any settings from default apart from the color of your computer.

Note that green is the most efficient color on the Perdix, so many divers change their computer’s display to all green to extend battery life. This is not required.