Note: I am only including ‘true’ technical diving computers; because there are some awful impostors on the market nowadays.  Manufacturers may simply boast that a computer offers multiple gasses and/or trimix capability, but that in itself does NOT make a computer ideal for modern technical diving.

I place emphasis on the choice of algorithm installed. This is critical for technical divers – and this is where manufacturers who insist upon using secretive, proprietary models fall woefully short. Proprietary algorithms aren’t easily predictable and cannot be replicated on most desktop deco planners – and this makes them a liability for carefully planned technical dives.

All of the computers I’ve listed use algorithms that feature on the most popular dive planning software; such as Multideco, V-Planner or GAP.

My list of factors needed in a ‘true’, modern technical diving computer:

  • Transparent and predictable algorithm (in sync with available technical dive planning software)
  • Five or more gas mixtures, including trimix and O2 up to 100%
  • Working depth (sensor reliability) below 100m
  • Recalculates ascent profile in missed stop scenarios (no ‘REFER TO TABLES’ or lock-out abandonment)
  • Significant user customization in the display and in-water information options
  • Bright, clear and logical screen/display (not requiring a torch or button pressing to illuminate)
  • Continued (free) firmware updates, to eradicate glitches and/or embrace evolving decompression  theories
  • An uncomplicated and intuitive user interface (UI)
  • Ability to redefine conservatism on-the-fly during the dive

Full Sized Technical Computers

Shearwater Perdix

  • Algorithm: Bühlmann ZH-L16C with Gradient Factors (VPM-B/GFS optional upgrade)
  • PC Link: SMART ready Bluetooth (dual mode 2.1/4.0)
  • No. Gasses: 5
  •  Depth Rating: 140m  (guaranteed sensor accuracy) / 260msw (crush depth)
  • Screen Type: 2.2″ (320×240 QVGA) colour LCD with always-on LED backlight
  • Battery:  User replaceable AA (100 hours in cave mode) or SAFT LS14500 (230 hours in cave mode)
  • Mounting:   Elasticated Straps or Integrated Bungee
  • Materials:   Injection moulded high tensile/rigidity nylon resin
  • Compass:  3-Axis, tilt compensated, digital compass
technical diving computer perdix

Shearwater remains, IMHO, the market leader for excellent technical diving computers; and the Perdix (released in late 2015) is their most capable unit to date.  It must have been a hard task to improve upon the awesome Petrel 2, but switching to an injected/ moulded case allowed Shearwater to substantially reduce housing bulk.

An improved clarity screen, even if slightly smaller than the Petrel 2’s, allows a 30% improvement in battery life. I particularly like that Shearwater opts for a user-replaceable AA (or SAFT LS14500) battery. These are easy to obtain in any remote corner of the globe and a boon for remote expeditions or in locations where mains power-supply for recharging may be unreliable. What makes Shearwater a very relevant technical diving computer is primarily the flexibility inherent in its firmware.

The in-water display allows a high degree of user customization; with excellent options like ‘GF99’ (the current gradient factor %) and ‘@+5’ (predicted deco 5 minutes in the future) giving the diver much better situational awareness during the course of a technical dive. Nearly all of the diving parameters are also changeable in-water, so you can add or remove gasses; even change your high gradient factor setting, on-the-fly to react to changing circumstances that may present themselves.

The computer ships with Bühlmann ZH-L16C GF…  and has the option to upgrade to VPM-B; which allows the computer to mate very well with the most popular technical dive planning software. Based in Canada, Shearwater has an excellent reputation for customer service. I know several divers who’ve received very rapid replacement units when a fault has occurred.

Firmware is available in multiple languages: English, French, Simplified Chinese, Traditional Chinese, German, Korean, and Japanese.  Shearwater provides a good dive logging software for PC or Mac, to which dive information is easily transferred via Bluetooth.  There are also non-manufacturer dive logging apps for Android or iPhone that sync seamlessly when uploaded. With a retail price circa $780USD, the Perdix is a monster computer for a very reasonable price.   Here’s a good review of the Perdix:  X-Ray Mag | Perdix Review

Earlier in 2017, Shearwater released an Air Integrated (AI) version of the Perdix.  It probably won’t have much interest from the technical diving community at this stage, but does fulfil demand from recreational divers.

Product Link:

Product manual:

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Heinrichs Weikamp OSTC 4

  • Algorithm: Bühlmann ZH-L16+GF and VPM-B (switchable during the dive)
  • PC Link: Bluetooth
  • No. Gasses: 5
  •  Depth Rating: 200m
  • Screen Type: 3.2″ (800 x 480 pixel) IPS LCD monitor
  • Battery:  Wireless inductive Qi charging Li-Ion  (40 hours in dive mode)(2 years stand-by mode)
  • Mounting:   Integrated Bungee
  • Materials:   Aluminum housing with Perlucor ceramic screen
  • Compass:  3D digital compass

ostc4 technical diving computer The OSTC4 is the Heinrichs Weikamp flagship model. It is uncompromising and innovative in the technology and features supplied. A high purchase cost ($1355) reflects high-end features such as; inductive charging and dual-algorithm processing.  It also has the most beautiful high-resolution screen on the market.

The computer features a powerful 32-Bit dual-core processor.  This offers it sufficient computing power to run BOTH the Bühlmann ZH-L16+GF and VPM-B algorithms simultaneously during dives. You can switch and/or compare whenever you want.  The Li-Ion inductive rechargeable battery is user changeable, which saves a lot of hassle when battery replacement intervals come.

I’d like to see some more diver information options on this computer; like the @+5, GF99 and GFSurf displays that Shearwater includes – as these can significantly aid the diver’s awareness and decision-making loops. Tactical in-water information display is one area where most tech computer manufacturers need to get more creative. After all, the intelligent information display is the main purpose of the computer; and what serious technical divers look for.

With the biggest, clearest display currently on the market, it enables a lot of valuable information to be displayed on a single, main screen during dives – although the text can still be a little petite for divers with weaker eyesight.  It has a wet connector for use with CCR and there is an option to get the hwHUD system.

Product Link:

Product Manual:

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Shearwater Petrel 2

  • Algorithm: Bühlmann ZH-L16C with Gradient Factors (VPM-B/GFS optional upgrade)
  • PC Link: SMART ready Bluetooth (dual mode 2.1/4.0)
  • No. Gasses: 5
  • Depth Rating: 140m (guaranteed sensor accuracy) / 300msw (crush depth)
  • Screen Type: 2.4” (320×240 pixels)  QVGA, Full-Color LCD with always-on LED backlight
  • Battery:  User replaceable AA (70 hours in cave mode) or SAFT LS14500 (160 hours in cave mode)
  • Mounting:   Elasticated straps
  • Materials:   CNC milled Delrin plastic with 5mm Lexan faceplate
  • Compass:  3D digital compass
Technical Diving Computer Shearwater-Petrel-2

The Petrel 2 is the predecessor of the Perdix and was released in 2014.  It follows in the footsteps of the original Petrel 1 (2012) and the older Predator.

The firmware and on-screen information options are all identical to the Perdix, but the Petrel 2 has a bulkier (milled delrin) casing, slightly higher battery usage (the Perdix uses 30% less battery) and slightly less refined LCD display quality.  The Petrel 2 is available with Fisher connector for CCR divers; there is a DiveCAN model for the JJ-CCR also. As with the Perdix, the firmware is often updated for free; Shearwater seems dedicated to constantly refining and improving on functionality. Perdix Petrel 2 dimensions

Comparison of Perdix (left) versus Petrel 2 (right) dimensions.

What makes the Petrel/Perdix exceptional for technical divers is that it will constantly re-calculate your decompression even if planned stops are missed.  This can make the unit dangerous for untrained divers, as it would permit far less than optimal ascent schedules in response to sloppy diving.  However, it won’t ever abandon you when things go wrong.  I think it’s unconscionable that any modern technical diving computer would ‘give up’ on the diver because of a stop violation, but some manufacturers do persist with that liability-driven mentality.

The Petrel 2 does feel like a ‘brick’ compared to the sleek, lightweight Perdix; although I personally like the reassurance of that rugged ‘milled from a solid block of Delrin plastic’ solidity.  My Petrel2 has been accidentally catapulted across a dive centre to smash onto the concrete floor – and the ‘thunk’ on landing caused immediate relief.  A lesser unit would have cracked.  On a negative side, the Petrel 2 does miss the option to use integral bungees (my preference).  I had to make my own adapters to make bungees work.

 Product Link:

Product Manual:

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TDC-3 MultiDeco

  • Algorithm: Bühlmann ZH-L16C w/GF, VPM-B, VPM-B/E (Extreme), VPM-B w/GFS (Gradient Factor Surface), and VPM-FBO (Fast Bail Out)
  • PC Link: WiFi (direct to internet cloud)
  • No. Gasses: 10
  • Depth Rating: 150m
  • Screen Type:  2.2″ (320 x 240 pixel) Color TFT LCD
  • Battery:  Dual (redundant) user-replaceable SAFT lithium 3.6v or 1.5v  alkaline AA
  • Mounting:   3mm bungee straps (optional straps)
  • Materials:   All metal alloy machined body, scratch-resistant screen
  • Compass:  3D digital compass

TDC-3 technical diving computer

The TDC-3 was released in 2018 by the creator of MultiDeco software, Ross Hemmingway. Not surprisingly, this computer features the most complete range of decompression algorithm options on the market – everything, in fact, that you’d find on the MultiDeco platform.

It has a number of unique features and innovations that deserve special consideration. Firstly, it uses dual/redundant user-replaceable batteries – not only giving very long battery life, but also minimising any risk of battery failure during a dive. The computer menus are also accessed via a dual system, You can either use the two main piezo buttons on the sides, or a 4-way tap method on the housing itself.

Given the designer’s expertise in dive planning software and deco algorithm implementation, the computer has some novel options for pre-designating up to four (4) custom pre-set ascent and/or bail-out plans.

The computer doesn’t have bluetooth, but instead incorporates full WiFi functionality. This means you can connect it directly to the internet for updates or dive logging via Cloud interface. Logs can be downloaded or viewed on any device using HTML5 browser software.

The unit is low profile, even with the extra battery swallowed within, and the display is clean and easy to read. I particularly liked that it gives both ascent and descent rates in a full meters/feet per minute format – I wish more computers would adopt that.

Product Link:

Product Manual:

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Ratio iXM3 Tech+

  • Algorithm: Bühlmann ZH-L16B w/GF and VPM-B
  • PC Link: USB and Bluetooth
  • No. Gasses: 10
  •  Depth Rating: 300m / 984ft (crush depth /  130m/426ft sensor precision
  • Screen Type: 2.8″ (144 dpi / 320×240 pixel) QVGA IPS
  • Battery:  USB rechargeable Li-Ion (20-50 hours in dive mode)(4-5 hours recharge)
  • Mounting:   elasticated straps
  • Materials:   POM C (Acetal Copolymer moulded resin plastic) and Mackrolon screen
  • Compass:  3D digital compass
technical diving comutr Ratio iX3M Tech

The iX3M Tech+ is the flagship of Ratio’s “Pro” technical computer range, is programmed for full trimix capability and comes loaded with features.

With all the effort to cram this computer with amazing software features (see below) what mystifies me is that Ratio persists in using the Bühlmann ZHL-16B algorithm when almost every other contemporary tech computer uses the later ZHL-16C version. It seems like an inexplicable oversight…

It has options to download additional integrated apps like a magnetometer, luxmeter, altimeter, moon calendar, chronometer, pitch/roll display, weather forecast and barometer. It also features an (optional) USB plug-in O2 analyser and has integral gas-blending software installed.

The unit is wireless air integration and illuminating colour-coded transmitters can be purchased. The illuminating transmitter LEDs are also color-coded to warn of gas pressure; Green = 100+ bar / Yellow = 50-100 bar / Red = 0-50 bar.  Some divers may find this useful, but I can’t help thinking all those lights would make you sparkle like the Las Vegas strip on a dark dive.

If you want the integrated GNSS (GPS, GLONASS, Beidou, Quasi-Zenith) system, it is available on the separate iX3M [Gps] Tech+ model.

Ratio also offers more economical models, restricted for nitrox or normoxic trimix diving only:

  • iX3m [PRO] Easy – 2 gasses (air/nitrox), 6x Bühlmann ZHL-16B pre-set (not user definable)
  • iX3m [PRO] Deep – 3 mixes (air/nitrox/normoxic trimix), 6x Bühlmann ZHL-16B pre-sets (not user definable) and 6x VPM-B pre-sets.

Recreational divers can set their own preferences for deep stops (standard or Pyle method) and can manually input/designate what method of safety stops they want to complete.  The computer also features visual, audible and vibration alarms.

Product Link:
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Divesoft Freedom Full Trimix

  • Algorithm: Bühlmann ZH-L16 w/GF
  • PC Link: USB
  • No. Gasses: 9 (unlock/upgrade from Bottom Timer to Air, Extended Range or Trimix)
  •  Depth Rating: 300m  operational depth (no guaranteed sensor accuracy depth stated) (crush depth 600m/2000ft)
  • Screen Type: Full color (2.4″ vs 2.2″)  TFT OLED display
  • Battery: USB rechargeable Li-Ion (no details given of battery life dive mode)(5 hours recharge)
  • Mounting:   Elasticated Straps or Integrated Bungee
  • Materials:   Aluminum housing
  • Compass:  None

Divesoft freedom technical diving computer

The Divesoft Freedom is available with varied firmware options; bottom timer, nitrox (1 gas >40%), advanced nitrox (3 gas >100%) and trimix (9 gas w/helium).  The four-button long/short/simultaneous-press user interface seems a little complicated to use, but I’ve heard it’s quite intuitive to learn.

The computer has an add-on extra O2 analyzer function and can link to CCR (it’s used as a standard with the (Liberty  CCR).  It is even loaded with a suite of basic games to help make your decompression stops pass quicker. Sadly, the website/manual is unclear on the expected battery duration on dives/standby. The Li-On battery charges via USB in 5 hours.

With that large OLED screen, multiple functions and vibrating alarms, I would be concerned that battery life might be noticeably less than other technical diving computers on the market.

Product Link:

Product Manual:

Heinrichs Weikamp OSTC PLUS

  • Algorithm: Bühlmann ZH-L16C with optional gradient factors
  • PC Link: Bluetooth Smart Ready (2.0 and 4.0)
  • No. Gasses: Sport edition: 3 | Tech edition: 5
  • Depth Rating: 120m
  • Screen Type: 2.4″ (320 x 240 pixel) IPS LCD monitor
  • Battery:  Pad Rechargeable Li-Ion (2-hour charge) or user replaceable AA
  • Mounting:   Integrated Bungee
  • Materials:   Aluminum housing with scratch-resistant borosilicate-glass panel
  • Compass:  3D digital compass

heinrichsweikamp ostc plusThe latest offering from Heinrichs Weikamp is compact and colourful. It offers a more economical alternative to the OSTC4, at just over half the cost (Sport:$765/Tech: $900) of the flagship model. The OSTC range is well-known for outstanding build quality, well-implemented firmware and great customer service. This new model follows in that tradition.

The OSTC PLUS is available in two firmware formats; Sport and Technical. The Sport firmware is limited to three gasses (>100% O2), whereas the Technical version has five gasses, including trimix. Users buying the Sport firmware can upgrade, at extra cost, at a later date.

The milled aluminium build is of very high quality and provides the unit with a high level of streamlined ruggedness.  The anodised aluminium housing is available in a choice of seven colours; black, orange, green, gold, blue, purple and silver/grey.

Heinrichs Weikamp doesn’t have the big distribution network that other, larger, computer manufacturers have;  so you tend to see less of them in use outside of Europe.

Note: The OSTC PLUS did make the news in January 2019, as a display model exploded at a dive show, causing injuries. In a statement released by Heinrichs Weikamp, the explosion was caused by incorrectly inserting a non-rechargeable SAFT 3.6v battery. The unit incorrectly identified this as a rechargeable Li-Ion battery and, when placed on the charging dock, proceeded to charge the battery. After several hours, that battery exploded within the unit. There has been a firmware fix to prevent this problem reoccurring and Heinrichs Weikamp has stated that only 1.5v Alkaline non-rechargeable or Li-Ion 3.6v rechargeable batteries should be used.

Product Link:

Product Manual:  Not Yet Available

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Dive Computer EU

  • Algorithm: Bühlmann ZH-L16C with Gradient Factors
  • PC Link: Bluetooth
  • No. Gasses: 10
  • Depth Rating: 130m (pressure sensor accuracy)
  • Screen Type: TFT LED Screen (320 x 240 pixel)
  • Battery:  Replaceable AA battery
  • Mounting:   5mm Bungee mount
  • Materials:   CNC-milled Polyacetal (Delrin, POM) and stainless steel 316L
  • Compass:  3D digital compass

deep6 triton's abacus

If you are confused, the name of this computer is the ““. Kinda weird because that’s just the website address.  In the USA and Canada it is sold and branded at the Deep6 “Triton’s Abacus“.

Manufactured in Europe, this is a pretty rudimentary but functional tech computer.  It runs the modern-standard Bühlmann ZHL-16C algorithm with Gradient Factor adjustments.

It has six different operating modes, catering for every type of diving you might want to do:

  1. Apnea Mode
  2. Extended Gauge Mode (with 4 stopwatches)
  3. Open Circuit Recreational
  4. Open Circuit Trimix
  5. Closed Circuit – Fixed Setpoint
  6. Pure Buhlmann – variable ceiling

At $600 fully loaded to trimix specifications, via Deep6, it represents one of the most economical full tech computers on the market.

Product Link (Global):

Product Link (US and Canada):

Product Manual:

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Underwater Technologies AV1

  • Algorithm: Bühlmann ZH-L16C w/GF
  • PC Link: USB
  • No. Gasses: 8
  •  Depth Rating: 200m  tested depth range (130m sensor accuracy depth)
  • Screen Type: Full color 2.4″ (320 x 240)  TFT OLED display
  • Battery: USB rechargeable Li-Ion (10-hour in dive mode)(5 hours recharge)
  • Mounting:   Elasticated Straps or Integrated Bungee
  • Materials:   Delrin housing and polycarbonate screen
  • Compass:  3D Digital Compass
AV1 technical diving computer
The Russian made AV1 is similar in size, display and basic functions to the Shearwater Petrel2.  It is available with a Fischer connector (the AV1F version) and custom heads are manufactured for use with the Inspiration Classic/Vision and Poseidon MKIV CCRs.  However, unlike the Petrel2, the AV1 uses a USB rechargeable Li-Ion battery which necessitates removing/replacing a waterproof cap during each charging cycle.  This dry connection does present a risk of flooding.

One nice feature on the AV1 is that the diver can access the full deco plan on a separate screen.  This allows a little more forward planning than only having a TTS and current stop information available.  It comes pre-installed with the game ‘Python’ to make decompression stops pass a little quicker.  The AV1 doesn’t have additional diver information like GF99, @+5 or real-time tissue saturation graphs. The majority of additional software functions are aimed at CCR divers, for whom this unit seems primarily focused.

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Poseidon Mk28

  • Algorithm: DCAP and Bühlmann ZH-L16 w/GF
  • PC Link: WiFi Access Point, Bluetooth, IrDA (surface only)
  • No. Gasses: 8
  • Depth Rating: 200m
  • Screen Type:  2.8” TFT  QVGA LCD (pixel info not given)
  • Battery: Integral USB rechargeable (no details given of battery life in dive mode or charging time)
  • Mounting:   Integrated Bungee
  • Materials:   Not listed on website
  • Compass:  Digital

poseidon mk28 technical diving computer

Firstly, Poseidon… if you are listening…. when you charge a whopping $2000 for an instrument, please do bother to put all pertinent technical information on your website and in your manual. Details specification on ‘small’ details like materials, screen resolution, battery life, charge time and available gas mixes. This information does make a difference to prospective purchasers.  We shouldn’t have to read to page 39 of the user manual just to find that it allows eight gas mixes.

The Poseidon Mk28 is first and foremost designed as a CCR computer, in particular for integration with Poseidon’s own range of rebreathers. Open Circuit use seems an afterthought, although the computer is fully functional through to OC Trimix.

There is a range of connecting cables as optional extras for configuring with Poseidon’s Se7en CCR, a CAN Bus connection, cables for the Poseidon Solid-State O2 Sensor or CPOD to allow use with any other brand of CCR.

It is claimed as “the world’s most powerful dive computer“, but I could find no specific details on Poseidon’s website to illuminate why that claim is made. It is probably the world’s most expensive technical computer.

The Mk28 includes a built-in GPS and full world map software. However, there are reports that the GPS system is exceptionally slow to gain satellite data and that significantly detracts from its usability.

I don’t see anything to justify the huge price tag of this computer, other than its functionality with Poseidon’s own rebreathers.

Product Link:

Product Manual:,4_20180704-ID-12751906-4a77-4526-aac2-fe41922715d7.pdf

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Seabear T1 **

  • Algorithm: Bühlmann ZH-L16C with Gradient Factors
  • PC Link: USB and NFC (near field communication)
  • No. Gasses: 8 (additional unlock required for trimix)
  •  Depth Rating: 130m (pressure sensor accuracy)
  • Screen Type: Full color 1.7″ OLED Screen (160 x 128 pixel)
  • Battery:  USB rechargeable Li-Ion battery, 4.2V, 900mAh (24 hours in dive mode / 2-3 hours to charge)
  • Mounting:   Bungee mount
  • Materials:   Delrin plastic housing  and scratch-resistant sapphire screen
  • Compass:  3D digital compass
seabear t1 technical diving computer

The Seabear T1 features the appropriate algorithms, robust housing and bright screen that you’d expect to find on a dedicated technical diving computer.  The biggest innovation with the T1 is the user interface (UI), which makes use of a unique push wheel to quickly scroll and select within the menus.

seabear t1 wheel ui

One of the other novelties of Seabear computers is the NFC (Near Field Communications) function – which allows communication between smart devices (i.e. your phone) and linking with online social media.

At present, there seems to be no option to install/unlock alternative deco algorithms (VPM-B or RGBM), but the user has full control over the gradient factors in the Bühlmann ZH-L16C model provided. When performing decompression, the Seabear T1 has the main screen and a second, detailed, deco info screen. I like that stops are counted in minutes and seconds.  This should be a standard on all tech computers; not because that level of resolution is critical for off-gassing, but rather – because it helps teams coordinate departure from stops on the ascent.

The Seabear T1 doesn’t seem to have much scope for divers to specify and customize their own information screens in dive mode. Personally, I’d rather have technical diving features like (Shearwater’s) GF99 and @+5 than integrated Facebook sharing… but that’s just me.

**Note: After the 2015 acquisition of the company there were some unconfirmed reports on social media of severe difficulties with obtaining service/aftercare. I’ve also heard mention that production of SeaBear computers is now discontinued – although I cannot find any authoritative reference or official news of that.

I’ve included this review only because the computer is still listed for sale on multiple websites – I suggest confirming with the retailer about the availability of current/future Seabear product support before making any purchase.

 Product link: None Available

Product Manual:  None Available

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 Watch Sized Technical Computers

Shearwater Teric

  • Algorithm: Bühlmann ZH-L16 with Gradient Factors
  • PC Link: Bluetooth Smart LE
  • No. Gasses: 5
  •  Depth Rating: 200m
  • Screen Type: 1.39″(400 x 400 pixel) Full Colour AMOLED
  • Battery: Rechargeable docking Li-ion Battery; Dive Mode 30+ hours / Watch Mode 50+ hours
  • Mounting:   watch-style
  • Materials:   Ballistic nylon polymer case and 316 Stainless bezel/buttons with sapphire crystal screen
  • Compass:  3D digital compass

shearwater teric technical diving computer

Shearwater energized the market with its release of the Teric in 2018.  This watch sized technical computer squeezes in all of the functionality and firmware that you’d be accustomed to seeing on their full-size models.

It has OC recreational, OC technical, CCR, gauge and freediving modes. You can connect up to two (2) AI transmitters for wireless gas tracking and the screen display is vibrant and easy to view even in glare conditions.

Whilst the Teric doesn’t have the vast suite of sports and outdoors features offered by its competitor, the Descent Mk1 (see below), it is more functional as a dedicated technical diving computer – especially in regards to the data options like; GF99, GFSurf, tissue compartment graphs etc.

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Garmin Descent Mk1

  • Algorithm: Bühlmann ZH-L16 with Gradient Factors
  • PC Link: Bluetooth Smart, ANT+ and Wi-Fi
  • No. Gasses: 6
  • Depth Rating: 100m
  • Screen Type: 1.2″ (240x 240 pixel) sunlight-visible, transflective memory-in-pixel (MIP)
  • Battery:  Rechargeable Li-Ion docking type: up to 19 days in watch mode, 10 days in smartwatch mode, 40 hours in dive mode and 20 hours in GPS mode4
  • Mounting:   Watch-style: Silicone or Titanium
  • Materials:   Fiber-reinforced polymer case with a stainless steel or Titanium bezel and scratch-resistant sapphire crystal screen
  • Compass:  3D digital compass

garmin descent mk1 technical diving computer

The Garmin Descent Mk1 is a full function trimix computer, with added functionality as a fully smartphone compatible (with smart notifications and controls) outdoors, fitness and sports watch.

Whilst the Teric is a dedicated technical diving computer with all of the excellent diving functionality you’d see in Shearwater’s full-size devices, the Garmin Descent Mk1 is much more of an all-rounder – and would appeal to those who also want the features of both a smart-watch and highly capable sports/outdoors instrument.

It features a vast array of sensors, including; GPS, GLONASS, Elevate™ heart rate monitor, barometric altimeter, compass, gyroscope, accelerometer and thermometer. These allow specific multisport operating modes, which can be linked to the internet via a smartphone, for swimming, cycling, golf, fitness tracking, running, and outdoors (hiking/climbing, mountain biking, skiing, snowboarding, rowing, jumpmaster and tactical). You can download digital maps onto the watch, for use with the abovementioned modes.

Additional apps can be installed via Garmin’s online store.

Product Link:

Product Manual:

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Ratio iDive Color Tech+

  • Algorithm: Bühlmann ZH-L16B w/GF and VPM-B
  • PC Link: USB
  • No. Gasses: 10
  • Depth Rating: 220mt / 721ft
  • Screen Type: TFT LED w/IPS, 1.3″ (240×240 pixel) 261 ppi
  • Battery: USB rechargeable Li-Ion (25 hours in dive mode)
  • Mounting: Polymer straps
  • Materials:  Sapphire Crystal screen with Stainless steel bezel and case.
  • Compass:  3D digital compass
ratio idive color tech+ technical diving computer

The iDive Color Tech+ is the new 2019 flagship of Ratio’s watch-sized computer range. It is programmed for full trimix capability and comes with many of the features you’d find on their full-sized iX3M range.

The top-of-the-range Color Tech+ comes with a sapphire crystal screen. This material is second only to diamond with respect to hardness and scratch-resistance and improves the depth rating of the Tech+ to 220m compared to the Easy and Deep variants which have mineral glass screens.

As with the iX3M, the iDive Color Tech+ opts for the Bühlmann ZHL-16B algorithm, which is an unusual decision that I cannot explain a reason for.

You’ll find it has all the standard Ratio gadgets: magnetometer, luxmeter, altimeter, moon calendar, chronometer, pitch/roll display, weather forecast and barometer. It also features an (optional) USB plug-in O2 analyser and has integral gas-blending software installed.

The unit is wireless air integration and illuminating colour-coded transmitters can be purchased. The illuminating transmitter LEDs are also color-coded to warn of gas pressure; Green = 100+ bar / Yellow = 50-100 bar / Red = 0-50 bar.  The tech community generally hasn’t adopted air-integration yet, so I doubt this would be a valuable functionality for many buying the Color Tech+. Also, for cave and wreck divers, all those sparkly transmitter LEDs are liable to be distracting in dark environments.

Ratio also offers more economical models, restricted for nitrox or normoxic trimix diving only:

  • iDive Color Easy – 2 gasses (air/nitrox), 6x Bühlmann ZHL-16B pre-set (not user definable)
  • iDive Color Deep – 3 mixes (air/nitrox/normoxic trimix), 6x Bühlmann ZHL-16B pre-sets (not user definable) and 6x VPM-B pre-sets.

Recreational divers can set their own preferences for deep stops (standard or Pyle method) and can manually input/designate what method of safety stops they want to complete.

Product Link:
Product Manual:
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Seabear H3 **

  • Algorithm: Bühlmann ZHL-16 with Gradient Factors (4 pre-sets)
  • PC Link: USB and NFC (near field communication)
  • No. Gasses: 8 (additional unlock required for trimix)
  •  Depth Rating: 130m
  • Screen Type: 1.7″(160 x 128 pixel) Color OLED
  • Battery:  Rechargeable 4.2V, 400mAh Li-Ion battery (12 hours in dive mode / 2-3 hours to charge)
  • Mounting:   watch-style
  • Materials:   316L stainless steel and scratch-resistant sapphire screen
  • Compass:  3D digital compass
technical diving computer seabear h3

The Seabear H3 was the first watch-sized true technical computer, released in 2014, but is now a generation behind the newest computers. It features both a 3D digital compass and altimeter – making it a good options for outdoor activities above-water also.  The UI seems simple, using 2 buttons with short/long press actions to navigate and select within the menus.

The big selling point for this tech computer is its lower cost compared to either the Teric or Descent Mk1.  It also has modern social media features’ where it can link to Android phones using the NFC technology; for instant uploading and sharing of dive logs.

**Note: After the 2015 acquisition of the company there were some unconfirmed reports on social media of severe difficulties with obtaining service/aftercare. I’ve also heard mention that production of SeaBear computers is now discontinued – although I cannot find any authoritative reference or official news of that.

I’ve included this review only because the computer is still listed for sale on multiple websites – I suggest confirming with the retailer about the availability of current/future Seabear product support before making any purchase.

Product link: None Available

Product Manual: None Available

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Not Currently Recommended

Scubapro G2

  • Algorithm: Uwatec ZHL-16 ADT MB
  • PC Link: USB and Bluetooth
  • No. Gasses: 8
  • Depth Rating: 120m / 394ft
  • Screen Type: TFT (Thin-Film Transistor) LCD 2.2in” (320×240 pixel)
  • Battery: USB rechargeable Li-Ion battery (50 hours)
  • Mounting:   Integrated bungee mounts or Elastomer strap
  • Materials:   Fiberglass-reinforced thermoplastic case with TR 55 transparent thermoplastic screen
  • Compass:  Digital Compass

scubapro g2 technical diving computer

The Scubapro G2 doesn’t make my list because they’ve opted for a proprietary in-house iteration of the Bühlmann ZHL-16 algorithm – the Uwatec ZHL-16 ADT MB (Adaptive Micro Bubble).

The creation of ZHL-16 ADT MB seems simply to empower a more expensive retail package that includes a heart rate monitor (HRM) and facilitates arbitrary deep-stop (PDIS) functionality that’s taken a hammering in contemporary scientific studies:

See: US Navy Experimental Dive Unit  (NEDU) technical report 2011-06: “Redistribution of decompression stop time from shallow to deep stops increases incidence of decompression sickness in air decompression dives”. Doolette, DJ; Gerth, WA; Gault, KA. (2011)  LINK

The ‘trend’ for deep-stop algorithms took a sudden U-turn when the 2011 NEDU study was released, and Scubapro/Uwatec seem a little slow keeping pace with the latest developments. Instead of using a dedicated bubble-model (dual-phase) algorithm, like VPM-B, they opted to bastardise a gas diffusion model into providing deep-stop results. Being a proprietary in-house project, nobody outside of Uwatec knows exactly how they achieved that – which isn’t reassuring for technical divers.

To date, there is no scientifically studied validation for heart-rate adaptive algorithms, which means that UWATEC has applied variable modifications to the inert gas uptake and elimination rates based on zero published or proven rationale.

“To my knowledge, there is no laboratory data to indicate how much, if any, adjustment should be made for nitrogen uptake and elimination in these situations.  […]  No doubt, the [ZHL-16 ADT MB] programmer simply entered some modifying factor into the algorithm and presents this as the gospel truth. This is nice for marketing but the modifications are guesswork, as far as I am aware. Computer makers do not perform laboratory research for their devices”.

Michael R. Powell (Dr Deco), M.S., Ph.D, NASA (retired)

In short, it’s a gimmick. Scubapro modified a well-proven base algorithm in order to implement unproven concepts; chiefly to appeal to divers who may be under a misguided impression that deep stops and heart rate are scientifically verified ‘improvements’ to decompression safety.

The downside to this marketing innovation is that the algorithm ceases to be predictable based on pre-dive profile and gas management planning (see my criteria in the opening paragraphs). It is also inconsistent with the algorithms provided on commercial deco planning software, and those used on the computers of other technical divers/team members.

Other than the algorithm choice and HRM, the Scubapro G2 doesn’t provide any functionality not evident on the leading technical dive computers listed. In respect to materials and screen technology, it seems a generation behind the latest generation of computers.

If Scubapro ever decides to offer a firmware upgrade that allowed installation of user-selectable open-source Bühlmann ZHL-16C and/or VPM-B/E firmware; then the computer might finally find it’s way onto my recommended list.

Until then, my view is that the Scubapro G2 devotes far more attention into showcasing marketing gimmicks, and far too little focus on providing reliable, proven and industry-consistent technical diving functionality.

Product link:

Product Manual:

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Suunto Eon Steel

  • Algorithm: Suunto Fused™ RGBM
  • PC Link: USB
  • No. Gasses: 10
  •  Depth Rating: 150m  operational depth (no guaranteed sensor accuracy or crush depth stated)
  • Screen Type: LCD TFT Display (320 x 240) with LED backlight
  • Battery: Rechargeable Li-Ion battery (20-40 hours)(30 days in standby)
  • Mounting:   Elastomer strap or optional bungee
  • Materials:   Brushed Stainless Steel bezel, composite body and Xensation™ glass display
  • Compass:  3-Axis, Tilt Compass
 suunto eon steel technical diving computer

I don’t really class the Suunto Eon Steel as a ‘true’ technical diving computer.  For a start, the Suunto Fused RGBM is a secretive beast and it’s hard to reliably plan dives with an algorithm that may modify itself as the dive progresses.

***I’ve heard rumors that Suunto may intend to release a firmware update for the Suunto Eon Steel that will allow installation of Bühlmann ZHL-16C algorithm***

Stay tuned for updates. The Suunto Eon stays off my recommended list until/unless that firmware upgrade happens.  Why?

I don’t like unpredictable algorithms.

I don’t like algorithms that might give me more decompression once in-water than I’ve planned for pre-dive. I have a pre-dive plan for my gas consumption for that dive, based on a pre-agreed ascent schedule.  I carry reserve gas, but using that reserve constitutes an emergency… not because my algorithm got ‘creative’ on me.  What can cause these digressions in decompression? According to Suunto:

  • Monitoring continuous multiday diving
  • Computing closely spaced repetitive diving
  • Reacting to a dive deeper than the previous dive
  • Adapting to rapid ascents which produce high microbubble (silent-bubble) build-up
  • Incorporating consistency with real physical laws for gas kinetics

As Suunto state: “Reduced gradient (variable) M-values based on diving habit and dive violations“.

Suunto interprets this as “additional safety”…. but for many technical divers it amounts to unpredictable behaviour.  If you carefully pre-plan a dive with X bottom time, Y depth and using Z gasses; the decompression schedule should remain constant.  Suunto RGBM will unilaterally, and without indication, increase that mandatory decompression if you momentarily exceed an ascent rate, drop a bit lower than a previous dive, or dive over multiple days.  But wait… I planned my deco…and my gas consumption… do I now have enough gas to do the deco stops that the Eon Steel mandates?

The ‘fused’ model itself is a splice between recreational/regular RGBM and a specific technical/trimix adaptation of the model.  Where and when do the models switch from one to the other?  We don’t know because Suunto doesn’t publish this modelling information.

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In general, serious technical divers want to understand how an algorithm functions and have the capacity to refine ‘deco curves’ to suit their preferences and unique individual needs.  This is impossible with Suunto Fused RGBM.  The only choice presented to divers is the level of conservatism (-2 Aggressive to +2 conservative).

This is very ‘recreational’ in approach… and not the level of sophisticated algorithmic manipulation that technical divers come to expect with models like Bühlmann ZH-L16 with full gradient factor control.

Because Suunto Fused RGBM is also a proprietary (commercially secretive) algorithm, you won’t find it featured on any of the popular decompression planning software like Multi-Deco, V-Planner, GAP or Decoplanner. You have to use Suunto’s quite limited dive planning software.  It also won’t fit in well with other technical divers who would probably be using  Bühlmann or VPM-B models.

The Eon Steel does boast 10 gas mixes.  I am pondering who needs 10 gas mixes for dives down to  150m.   It reminds me of that scene from the comedy movie “There’s Something About Mary”:

Hitchhiker: You heard of this thing, the 8-Minute Abs?

Ted: Yeah, sure, 8-Minute Abs. Yeah, the exercise video.

Hitchhiker: Yeah, this is going to blow that right out of the water. Listen to this: 7… Minute… Abs.

Ted: Right. Yes. OK, alright. I see where you’re going.

Hitchhiker: Think about it. You walk into a video store, you see 8-Minute Abs sittin’ there, there’s 7-Minute Abs right beside it. Which one are you gonna pick, man?

Ted: I would go for the 7.

Hitchhiker: Bingo, man, bingo. 7-Minute Abs. And we guarantee just as good a workout as the 8-minute folk.

Well…. there you go folks….  “10 Gas Mixes“…

If the Suunto Eon Steel offers “fully customization”, how can I install/upgrade  Bühlmann ZH-L6C w/GF or VPM-B to match what my technical diving team/buddy use?  I cannot…

Suunto software is also chock full of ‘obstructive safety protocols that have no part in technical diving.  They may be useful for keeping unaware or incautious recreational divers safe, but those protocols pose real issues for technical divers.

An example of this is the Suunto “Algorithm Lock”, whereby the computer automatically shuts you out for 48 hours if you violate a decompression ceiling for more than 3 minutes.  The screen will display only an ‘ERROR’ message.

If, as a technical diver, you were in a position where you had to ascend beyond a designated stop (I can think of a few examples of those), the computer algorithm would simply abandon you.  Compare that to other tech computers, which would re-calculate the ‘next best’ decompression schedule to get you safely to the surface.

Modern technical diving computers should never abandon the diver in-water.

Suunto computers always add a safety stop.  This means that when in decompression, the TTS (time-to-surface) always reads 3 minutes longer than is actually demanded by the algorithm.  It’s annoying… and I’ve seen it confuse more than a few novice technical divers.  Do I have 5 minutes of decompression to complete or 8 minutes…. why is this unclear?

The Suunto Eon Steel allows a choice between 4 dive screens.  It cannot be fully customized like, for instance, a Shearwater Perdix user can select which information is displayed, and where on the screen they want it.

Suunto uses the term “full customization’ throughout their advertisements and product literature for the Eon Steel.  I find it one of the least customizable technical computers on the market.

Overall, I feel that the Suunto Eon Steel markets itself mostly to recreational divers who want a computer that “appears technical” but actually operates like a limiting recreational diving computer.

It’s almost “faux-tech’; a computer that looks great on recreational dives, but falls very short on technical dives.

A modern technical diving computer simply cannot give you an “ERROR” screen if you are forced to adopt an ascent profile that varies from the ideal. Nor should it amend the decompression algorithm based on “diving habits” and “dive violations” once decompression and gas plans have been committed to by the technical diver.

Product Link:

Product Manual:

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Other informational sidemount equipment lists:

About the Author

andy davis technical diving philippines

Andy Davis is a RAID, PADI TecRec, ANDI, BSAC and SSI qualified independent technical diving instructor who specializes in teaching advanced sidemount, trimix and wreck exploration diving courses across South East Asia.  Currently residing in ‘wreck diving heaven’ at Subic Bay, Philippines, he has amassed more than 9000 open circuit and CCR dives over 28 years of diving across the globe.

Andy has published many magazine articles on technical diving, has written course materials for dive training agency syllabus, tests and reviews diving gear for major manufacturers and consults with the Philippines Underwater Archaeology Society.

He is currently writing a series of books to be published on advanced diving topics.  Prior to becoming a professional technical diving educator in 2006, Andy was a commissioned officer in the Royal Air Force and has served in Iraq, Afghanistan, Belize and Cyprus.


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