Nullzeit

A decompression secondary display for the Apple Watch Ultra.

Not a certified dive computer — a secondary display.

No EN 13319 approval, no redundancy. Always dive with an independent, certified dive computer and follow it and your training. If the two displays disagree, the certified computer wins — every time.

Request beta access Read the manual

Apple Watch Ultra 3 with Ocean Band showing the Nullzeit decompression display: 33 m depth, first stop 3 m for 2 minutes, 5 minutes to surface

What it does today

On your wrist, during the dive

Live depth, dive time and water temperature from the Ultra's native depth sensor
ZH-L16C tissue model (Bühlmann, gradient factors): no-deco limit, stops, ceiling, time-to-surface
Safety-stop guidance, ascent-rate and depth-limit warnings — traffic-light colours plus distinct haptics
Zero-touch under Water Lock: everything readable by glance, the crown does the rest
Logbook with dive profile, tissue view, built-in manual and demo dives
No internet, no phone, no account needed — works on the boat, on the island

What it is not

Not a dive computer — not certified to EN 13319, no pressure-chamber qualification yet
Not a primary or backup instrument: never base a diving decision on it
Not a finished product — this is a development beta for divers who want to help test

Built like an instrument, labelled like a beta

179 automated tests, including cross-checks against published Bühlmann table values
Requirements specification with full traceability — written as the input for a future conformity assessment
Honest-values design: the display shows only what the pipeline measures; after any fault it falls back to the conservative state and says so — including an explicit "do not trust" instead of a guess
Developed by a certified diver and software engineer with ten years of automotive functional-safety background (ASIL-B release responsibility)
Staged wet-test protocol: bench → pool (field-verified) → confined water → guided recreational dives, always next to a certified reference computer

Example screens

READY screen with gas, gradient factors and sensor limit — Pre-dive: gas, GF, sensor limit — and the disclaimer

Dive screen showing depth and no-deco limit — In the dive: depth rules the screen

Decompression screen with first stop and time to surface — Deco: first stop and time-to-surface

Red ABOVE STOP directive instructing to descend — A stop violation: the red directive names the action

SLOW ascent-rate takeover — Ascending too fast: SLOW, with live rate vs. max safe

Tissue saturation view — Tissue loading, compartment by compartment

After the dive: profile, stats and the no-fly estimate

Manual page with QR code — Built-in manual — QR opens it on the phone

The road to a real dive computer

The honest path, stage by stage:

Today: an uncertified app reading depth to 6 m — Apple's publicly available shallow-depth API.
After Apple's development approval: an uncertified app to 40 m — internal testing and validation only (application filed July 2026).
After Apple's distribution approval and EN 13319 certification: a dive computer to 40 m, sold in the App Store.

Every stage is real engineering, real validation and real money — and it is the plan. Until then, every build says what it is: a secondary display.

Get involved

Dive the beta

You dive an Apple Watch Ultra? Test Nullzeit as a secondary display next to your certified computer and tell us what you see — every structured debrief makes the instrument better.

Request beta access

Back the certification path

You bring EN 13319 or dive-instrument experience, run a dive school or a test lab — or you want the finished dive computer to exist and are willing to support it as a future customer? Let's talk.

Offer support