Recreation Model — Bühlmann ZHL-16C · DepthPlanner / DiveRobotix

DIVECOMMAND

by DiveRobotix LLC

Recreational Depth Planner · Bühlmann ZHL-16C · GF 40/85

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Algorithm

Bühlmann ZHL-16C

Same model used by Suunto, Shearwater, Garmin & Scubapro computers.

Gradient Factors

GF 40 / 85

Conservative setting. Shorter NDLs than most computer defaults — intentionally.

Compartments

16 Tissues

All 16 compartments tracked continuously across every dive and surface interval.

What Are Gradient Factors?

Gradient Factors (GF) are two numbers that control how conservative the Bühlmann algorithm is, written as GF Low / GF High. GF High (85) means tissues are allowed to reach 85% of their theoretical M-value limit before the algorithm flags a violation. Lower = more conservative = shorter NDLs. Higher = more aggressive = longer NDLs but less safety margin.

GF Low (40) controls the depth of the first decompression stop if a deco dive occurs. For recreational no-decompression diving, GF Low has minimal impact — GF High drives the NDL.

Why GF 40/85 on This Planner?

This planner uses GF 40/85 — the default medium conservatism setting on Shearwater, Garmin, and Suunto dive computers. This means the planner and your dive computer are working from the same assumptions, making it a true companion for pre-dive planning.

This planner will produce NDLs that closely match your Shearwater at factory GF settings. If you have changed your computer to a more aggressive GF, expect the computer to show a longer NDL than this planner.

⚠ Warning

Never adjust gradient factors to make a profile more aggressive without formal decompression theory training. Increasing GF High toward 95-100 allows tissues to approach their theoretical maximum overpressure — significantly increasing DCS risk. GF 40/85 matches Shearwater factory defaults and is the recommended setting for recreational diving.

Altitude Sea Level Enable Altitude Corrections

Water Type Salt Water Salt Water

Units Imperial ft / psi

⚙ Technical Mode OFF

Enable custom GF · multi-gas · deco ceiling

GASSelect Breathing Gas

Custom O2 % (16–100)

O2 % (18–100)

He % (0–80)

Gradient Factors TECH

Controls decompression conservatism · Factory: GF 40/85

Show

GF Low — first stop

Lower = deeper first stop · Conservative: 20–35

GF High — surface ceiling

Lower = more surface time · Conservative: 70–80

DIVE 1Depth & Bottom Time

Select a breathing gas above to begin.

Multi-level dive

Bottom Time (min)

⚠ Depth ≥ 100ft — Narcosis risk. Verify diver experience.

NITROGEN STATUS ▼ 16-Compartment Detail

Compartment 1 · HT -- ▲ LEADING

Bühlmann ZHL-16C — 16 Tissue Compartments
Your body absorbs nitrogen at different rates in different tissues. Fast compartments (5 min half-time) saturate and clear quickly — they drive your NDL on short dives. Slow compartments (635 min) accumulate nitrogen over multiple dive days.

Green = safe · Amber = approaching limit · Red = at or over limit. The leading compartment controls your NDL right now.

📉 DIVE PROFILE

CNS O₂

🧇

SAFETY STOP: 3–5 min at 15 ft on every dive ≥30 ft. Max ascent 30 ft/min.
Nitrox: MOD enforced · EAD used for depth lookup.

SURFACESurface Interval

N₂ Load After Dive 1 --%

Complete Dive 1 to see nitrogen status.

Surface Interval Timer

Start the timer when you surface. It tracks your elapsed SI and updates your adjusted NDL in real time.

Surface Interval Elapsed

00:00

MM:SS

Until NDL ≥30min

--:--

Status

WAITING

N₂ LOAD — CLEARING IN REAL TIME

--%

✓ MINIMUM SI REACHED

Or enter SI manually

Hours

Minutes

N₂ Load After SI

—

Duration

—

MIN SISurface Interval Planner

Pick your next dive depth — see exactly how much bottom time you get at each surface interval.

Dive 2 Depth

DIVE 2Next Dive — Adjusted NDL

Multi-level dive

Bottom Time (min)

CNS O₂

SURFACE 2Surface Interval 2

Hours

Minutes

N₂ Load

—

Duration

—

DIVE 3Next Dive — Adjusted NDL

Bottom Time (min)

CNS O₂

GAS Gas Planning Show

SAC Rate (psi/min)

RMV (cu ft/min)

SAC Benchmark

6 Elite10 Tech16 Rec24+ New

Record your tank pressure at the start and end of a dive to calculate your SAC rate.

Start Pressure (psi)

End Pressure (psi)

Avg Depth (ft)

Dive Time (min)

Tank used on that dive

Volume (cu ft)

Working Pressure (psi)

Tank

Tank Configuration

Select a tank below.

Volume (cu ft)

Working Pressure (psi)

Fill Pressure (psi)

Planned Depth (ft)

Bottom Time (min)

Gas Rule

Stage & Deco Bottles

Bottle 1 — Stage / Travel Mix (optional) Disabled

O2 %

He %

Switch (ft)

Cu ft

Fill (psi)

Reserve (psi)

Bottle 2 — Deco Gas (EAN50 / O2) (optional) Disabled

O2 %

He %

Switch (ft)

Cu ft

Fill (psi)

Reserve (psi)

Bottle 3 — Shallow Deco (O2) (optional) Disabled

O2 %

He %

Switch (ft)

Cu ft

Fill (psi)

Reserve (psi)

      Rule of thirds: 1/3 out · 1/3 back · 1/3 reserve. Always confirm with your dive buddy.
    

LOGDive Plan Summary

HIST Dive History — Multi-Day N₂ Tracking Show

Residual N₂ Load Entering Today’s Dive

No previous dives logged — starting with clean tissues.

✈️

NO-FLY TIMER

Single dive: 12 hr minimum before flying

Elapsed

0:00

h:mm

Minimum

hours

Clear at

--:--

local time

✓ GOOD TO FLY

Single dive: 12 hours minimum · Multi-dive or multi-day: 18 hours · Deco dives: >18 hours
When in doubt: wait 24 hours · Source: DAN / UHMS Flying After Diving Workshop

GEAR Pre-Dive Equipment Checklist Show

Check off each item before entering the water. Tap any item to mark it complete.

WEIGHT Ballast Weight Calculator Show

Estimates starting ballast weight. Always verify buoyancy in shallow water before your dive.

Body Weight (lbs)

Gender

Wetsuit / Exposure

Tank

Experience Level

Body Type

FLY Flying After Diving Show

Select Dive Profile

Single no-decompression dive

12-hour minimum

Multiple dives / multi-day diving

18-hour minimum

Dives requiring decompression stops

>18 hrs — recommend 24 hrs

Start when you surface from your last dive  ·  Timer persists if you reload

Elapsed

0:00

h:mm

Minimum

12

hours

Clear At

--:--

local time

✓ GOOD TO FLY

      Source: DAN / UHMS Flying After Diving Workshop Consensus  · 
      Single no-deco: 12 hr  ·  Multiple / multi-day: 18 hr  ·  Deco: >18 hr  ·  When in doubt: wait 24 hours
    

Educational Use Only
Not a substitute for dive training or a certified dive computer. Bühlmann ZHL-16C algorithm (GF 40/85). Always dive within your certification limits. Never dive alone.
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