A decompression secondary display for the Apple Watch Ultra.
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.
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
Standalone, offline, yours
No phone. No cloud. No account.
Nullzeit runs entirely on the Apple Watch Ultra — there is no companion iPhone app to install, nothing to pair or sync, no sign-up. Leave the phone in the dry bag.
Works with zero signal
There is no network code on the watch at all — no internet, ever. On the boat, on a remote island, deep on the reef: it behaves identically, because nothing it does depends on a connection.
Your dives stay yours
Every dive is stored only on your watch. Nothing is uploaded, there is no tracking. When you want your data elsewhere, you export it yourself as an open UDDF file the rest of the diving world reads — data sovereignty by design, not as a setting.
Built like an instrument, labelled like a beta
- 291 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
Watch it dive
The guided demo dive, rebuilt in HTML
No video, no GIF — the animation is the page itself: an HTML re-creation of the app's guided demo dive, a complete 30 m decompression dive at ×60, the same script the watch plays hands-free. Descent, no-deco countdown, the amber DECOMPRESSION badge, the stops at 6 m and 3 m, the safety stop, the surface.
Like every demo in Nullzeit it wears the DEMO ×60 badge the whole time — a demo screen can never be mistaken for a live dive. The values here are approximated for the web; on the watch the demo runs the real ZH-L16C model, and an interactive demo puts the depth on the Digital Crown.
Example screens
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 EN 13319 certification of the app + watch as one measuring system by an independent lab, and Apple's distribution approval: a dive computer to 40 m, sold in the App Store — depth and time measurement certified; what that does and doesn't cover is spelled out below.
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.
What “certified” will mean — and what it won't
EN 13319 is an instrument standard: what gets certified is the measuring chain — app and watch tested together as one depth-and-time instrument, from sensor to display. When Nullzeit gets there, we will publish the certificate and its exact scope.
And what no certificate covers, on any dive computer in the world: the decompression algorithm. No standard for deco software exists — every manufacturer ships it on its own responsibility. Ours is no exception, so we validate it the verifiable way: a documented core whose test expectations come from an independent second implementation of the same equations — and we say so, instead of letting “certified” imply more than it means.
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.
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.