▚ THE SLATE ▚

Dive Glossary

The words on the boat, in the forum, and stamped on the cylinder — explained plainly. Gear-research context, not dive instruction: anything touching planning points you back to your training and DAN.

Air integration

PRESSURE ON YOUR WRIST

A transmitter on the first stage sends cylinder pressure to your computer, adding gas-time-remaining math and auto-logged SAC. Costs several hundred dollars over a capable SPG; most divers who pay it stop looking at hoses entirely. Keep an analog backup anyway — batteries are batteries.

AL80

THE RENTAL-FLEET STANDARD

The aluminum 80-cubic-foot cylinder under most warm-water operations — fatter and taller than a steel HP100, slightly negative full, buoyant near empty. That end-of-dive float is the reason your last 10 minutes need attention to weighting. The blueprint tee in our shop is this tank, dimensioned.

ATA

PRESSURE BY DEPTH

Atmospheres absolute — total pressure counting the air column plus water. Surface is 1 ATA; every ~10 m of seawater adds another, so 10 m is 2 ATA and 20 m is 3 ATA. Boyle’s law follows: the air in your BCD and your gas consumption both track ambient pressure. Educational framing only; planning belongs to training.

Back-inflate BCD

TRIM-FORWARD JACKET ALTERNATIVE

A BCD with the bladder behind you instead of wrapped around your torso — better horizontal trim than a jacket, more familiar harness than a full backplate-and-wing. The middle step on the jacket-to-wing conversion path.

Backplate & wing

THE MODULAR SETUP

A metal plate, continuous-webbing harness, and a donut bladder sized to your cylinder — the configuration technical diving standardized and recreational trim-chasers adopted. Packs light for travel after swapping to an aluminum plate. See the jacket-vs-wing decision page for the honest tradeoffs.

Buddy check (BWRAF)

THE FIVE-POINT PRE-DIVE

The classic head-to-toe mutual check before entry — BCD, Weights, Releases, Air, Final okay. Agencies phrase the mnemonic differently; the five checks are universal. Our pre-dive tool renders it as a proper slate, tailored to boat/shore and gas.

Bühlmann ZHL-16C

THE OPEN ALGORITHM

The published dissolved-gas decompression model most modern dive computers implement, usually with gradient factors for tunable conservatism. Its openness is the selling point: predictable, documented behavior that Shearwater, Garmin, and others share. See our Bühlmann-vs-RGBM decision page for how it differs in practice.

Buoyancy check

THE SURFACE WEIGHT TEST

The standard check: at the surface with an empty BCD holding a normal breath, you should float at eye level and sink slowly on exhale. It calibrates your ballast to your actual gear that day. Procedure belongs to your training; we cover the gear variables that change the answer.

DCS / the bends

OFF-GASSING GONE WRONG

Decompression sickness: bubbles forming from dissolved inert gas when pressure drops faster than tissues can release it. It is the risk the entire NDL/ascent-rate/safety-stop system exists to manage. Gear research context only — prevention and response are training and medical topics (DAN is the canonical resource divers cite).

DIN

THREADED REG FITTING

The valve standard where the regulator screws into the cylinder valve, capturing the o-ring inside the connection. Rated to higher pressures and standard in Europe and technical diving. US travelers carry a yoke adapter; our DIN-vs-yoke page has the decision table.

Finger spool

THE DSMB’S OTHER HALF

A palm-size spool of line — commonly 15–30 m — that pairs with a DSMB for mid-water deployment. Simple, unjammable when used right, and one of the highest value-per-dollar items in the accessories bay.

First stage

TANK-TO-HOSE REDUCER

The regulator half that mounts on the valve and drops cylinder pressure to intermediate pressure for the hoses. Piston vs diaphragm architecture, port count/angles, and environmental sealing live here — it is the component that decides cold-water fitness.

Giant stride

THE BOAT ENTRY

The standard big-step entry off a boat deck or dock: one long stride out, hand on mask and reg, scissor the legs closed on splash. The moment fins, mask straps, and badly stowed octos reveal their quality. Backroll is its RIB-and-panga sibling.

Gradient factors

TUNING CONSERVATISM

A pair of percentages (like 40/85) that scale how close a Bühlmann computer lets you get to theoretical tissue limits — lower numbers, bigger safety margin, shorter NDLs. Mid-range computers expose simple conservatism steps; enthusiast units expose the raw GF pair. Change them only with training that explains what they do.

Hydro (hydrostatic test)

THE CYLINDER PRESSURE TEST

The periodic pressure test cylinders must pass — in the US, every five years, stamped into the crown — alongside more frequent visual inspections (VIP stickers). Fill stations refuse out-of-date tanks. A reason we treat cylinders as local-shop purchases, never shipped offers.

IP (intermediate pressure)

≈ 9.5 BAR OVER AMBIENT

The pressure a first stage feeds the hoses — typically around 9–10 bar (≈135 psi) above ambient. Service techs read IP with a gauge to diagnose creep or drift; a wandering IP is the classic “your reg is due” tell. One of the few numbers on a service invoice worth understanding.

Lift capacity

BCD BUOYANCY RATING

How much buoyant force a BCD bladder provides, in pounds or newtons — recreational singles setups commonly run 22–35 lb. Enough must float your rig at the surface with margin; grossly oversized wings just add drag and taco. Match lift to your cylinder and exposure suit, not to bigger-is-safer instinct.

MOD

NITROX DEPTH CEILING

Maximum Operating Depth: the deepest you can take a given oxygen fraction before ppO2 exceeds your planned limit — for EAN32 at ppO2 1.4, about 33–34 m. It is the number you write on the cylinder band after analyzing a nitrox fill. Set by your training and gas, never by a website.

Narcosis

THE “MARTINI EFFECT”

A reversible, depth-related impairment from breathing nitrogen under pressure — divers describe fuzziness, tunnel focus, or giddiness that fades on ascent. It is one reason recreational depth limits exist and one argument you will see in deep-computer marketing. Managed by training and conservative planning, not by gear purchases.

NDL (No-Decompression Limit)

THE REC-DIVING CLOCK

The time a dive computer estimates you can stay at your current depth and still ascend directly to the surface without required decompression stops. Recreational computers display NDL front and center — it shrinks as you go deeper and recovers as you ascend. Different algorithms call NDL differently, which is why buddies with different wrists disagree.

Neutral buoyancy

HOVERING

The state where you neither sink nor rise — the core skill recreational diving is built on and the thing every BCD, weight, and exposure decision either helps or fights. Gear cannot buy the skill, but badly weighted gear can absolutely prevent it.

Nitrox / EANx

ENRICHED AIR

Breathing gas with more than 21% oxygen — EAN32 and EAN36 are the standard recreational blends. Less nitrogen means longer no-stop times on repetitive mid-depth days, traded against an oxygen depth ceiling (MOD). Requires the cert, an analyzer, and the green-and-yellow band culture of labeling every fill.

No-fly time

OUR NAMESAKE

The recommended wait between your last dive and boarding a flight, while residual nitrogen clears at cabin altitude pressures. Common agency guidance runs about 12–18 hours after a single dive and 18–24+ after repetitive days — always follow YOUR computer, agency, and DAN guidance, not a t-shirt. We named the site after it because that grounded window is when divers read gear reviews.

O-ring

THE TINY TRIP-ENDER

The rubber seals throughout your kit — valve face, hoses, camera housings, light bezels. A blown valve o-ring hisses a dive dead in seconds, which is why a $15 assortment with picks and silicone lives in every save-a-dive kit. Match sizes and materials; nitrox service has its own compatibility rules.

O2 toxicity

WHY MOD EXISTS

Oxygen becomes toxic to the central nervous system at high partial pressures, with convulsion risk underwater — the hard reason nitrox has depth ceilings and fills get analyzed and logged. A training-and-planning topic; gear’s role is honest analyzers and computers that display ppO2 correctly.

Octopus (octo)

THE YELLOW BACKUP

Your backup second stage for sharing gas — conventionally high-visibility yellow on a longer hose, stowed where a buddy can find it. The nitpick that outs a fake diving graphic: the octo is yellow, the primary is not.

Off-gassing

NITROGEN LEAVING TISSUES

The slow release of dissolved inert gas from body tissues as ambient pressure drops — during ascent, safety stops, surface intervals, and the hours after diving. Computers model it continuously; the no-fly clock exists because off-gassing keeps running long after you towel off.

ppO2

THE OXYGEN-LIMIT NUMBER

Partial pressure of oxygen: the oxygen fraction times ambient pressure in ATA. Recreational nitrox planning typically limits it to 1.4 (working) with 1.6 as a contingency ceiling — the numbers behind every MOD table. Computers with nitrox modes display it live.

Regulator service

THE SCHEDULED REBUILD

Periodic overhaul — seats, o-rings, filters, IP check — on the schedule your manufacturer specifies (annual or every-two-years programs are common; some brands count dives). Skipping it to save $150 on the device that makes water breathable is the false economy of the sport. Our pre-dive tool tracks the dates; your manual sets them.

RGBM

SUUNTO’S CONSERVATIVE MODEL

Reduced Gradient Bubble Model — the proprietary algorithm family Suunto computers run. It factors bubble mechanics and tends to shorten NDLs on repetitive and reverse-profile days compared with Bühlmann implementations. Not wrong, just opinionated; know which voice your wrist speaks before a liveaboard.

RMV

SAC’S VOLUME COUSIN

Respiratory Minute Volume: gas consumption expressed as actual volume per minute (litres or cubic feet), independent of cylinder size. Convert SAC to RMV and you can plan any tank; that portability is why gas-planning nerds prefer it.

SAC rate

AIR FUEL-ECONOMY

Surface Air Consumption: how fast you breathe gas, normalized to surface pressure, usually in bar/min or psi/min. Track it across dives and it becomes the single most honest fitness-and-relaxation metric in your logbook. Air-integrated computers calculate it automatically; a wristwatch, SPG, and arithmetic get you the same number.

Safety stop

3 MINUTES AT 5 METRES

A voluntary pause — commonly three minutes around five metres — at the end of a recreational dive to give dissolved nitrogen extra time to leave slowly. It is the little plateau on every well-shaped dive profile, and the moment an end-of-dive-buoyant aluminum tank tries to float you. Your training agency’s guidance governs; a computer just counts it down.

Save-a-dive kit

TRIP-RESCUING SPARES

The pouch of o-rings, mouthpiece, zip ties, fin strap, mask strap, silicone, and tools that converts a gear failure at the dock into a five-minute fix. Costs less than one blown charter. Our free checklist builds one properly.

Second stage

THE MOUTHPIECE VALVE

The demand valve you breathe from: it opens on inhalation, closes after, with a purge button and exhaust tee. Cracking effort, venturi assists, and adjustment knobs are the comfort features reviews obsess over — rightly, since you feel every breath.

SMB / DSMB

SEND UP A BAG

Surface marker buoy — the bright tube you inflate to mark your position; the delayed version (DSMB) gets shot from depth on a spool before ascent so boats know where you are coming up. On many boats it is required kit. Practice deployment with an instructor before it matters.

SPG

SUBMERSIBLE PRESSURE GAUGE

The analog gauge on your HP hose reading cylinder pressure, red-zoned below about 50 bar. Beloved for having no battery to die. Our reading-progress dial on article pages is styled after one — 0 to 350 bar, needle sweeping toward reserve.

Steel vs aluminum (cylinders)

THE BUOYANCY ARGUMENT

Steel stays negative full-to-empty and packs more gas per size; aluminum is cheap, everywhere, and floats near empty. It changes your lead, your trim, and your end-of-dive handling — full decision page in the compare deck.

Surface interval

THE BETWEEN-DIVES CLOCK

Time spent at the surface between dives, during which tissues off-gas and your computer credits you back no-stop time. Longer intervals mean friendlier NDLs on the next drop. Also the cultural institution where gear arguments happen — this site is written for exactly that hour.

Thermocline

THE COLD LAYER

The abrupt boundary where water temperature drops — visible as a shimmer, felt as a slap. The reason quarry divers own 7 mm suits and hoods for August, and our name for the site’s mid-depth teal.

Trim

HORIZONTAL BODY POSITION

Your orientation in the water — flat and horizontal is the efficient, reef-safe default. Gear placement (tank position, weight distribution, wing vs jacket) sets the baseline your technique refines. The word doing the most work in every BCD review we publish.