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For the watch dive computer: an Apple Watch Ultra or Ultra 2 paired with an iPhone running iOS 17 or later. The Ultra is the only Apple Watch with the EN13319-certified depth sensor required for diving.

For the iPhone logbook app: any iPhone running iOS 17 or later. You can import dives from Suunto or UDDF files and use all logbook features without a Watch Ultra.

For the macOS app: a Mac running macOS Sonoma (14.0) or later.

The free tier gives you access to the full Bühlmann ZHL-16C algorithm, all safety alerts, and the complete logbook — limited to 1 dive per day.

Pelagic Pro (£4.99/mo) removes that limit and adds unlimited dives, iCloud sync, and advanced planning tools. The macOS app is included free with every Pro subscription.

Download Pelagic on your iPhone from the App Store. Open the Watch app on your iPhone, scroll to Available Apps, find Pelagic and tap Install. The app will appear on your Watch within a minute or two.

On your Watch, open Pelagic from the app grid and follow the on-screen prompts to grant water submersion permission — this is required for depth sensing.

No. The Watch app operates fully offline — depth sensing, decompression calculations, alerts, and data recording all work without any connection. Your dive is saved locally and syncs to iPhone when you surface and your Watch reconnects.

Pelagic uses Bühlmann ZHL-16C with Gradient Factors — the same algorithm used by Shearwater Research, Subsurface, and many other leading dive computers.

It models nitrogen loading across 16 tissue compartments and calculates your No Decompression Limit (NDL) continuously throughout the dive. Gradient Factors let you tune conservatism from more conservative (20/70) to more liberal (60/95).

Pelagic is designed for recreational diving — Open Water through Advanced, including Nitrox. The algorithm has been validated against established reference implementations and produces results consistent with other Bühlmann ZHL-16C computers.

That said: no app replaces proper dive training. Always dive within your certification level, with a qualified buddy, and exercise personal judgement.

Pelagic supports nitrox from EAN21 (air) through EAN40. You configure your O₂ fraction and PO₂ limit in Settings before the dive. The app will automatically calculate and display your Maximum Operating Depth (MOD) and alert you if you descend below it.

Gradient Factors (GF) control how conservative the algorithm is. Pelagic maps a single conservatism slider to GF presets:

• −2 (most conservative): GF 20/70 — used by technical divers
• 0 (default): GF 40/85 — balanced recreational setting
• +2 (least conservative): GF 60/95 — matches many agency tables

If you're unsure, leave it at the default. Ask your instructor if your training agency recommends specific GF settings.

NDL varies between computers based on algorithm variant, gradient factor settings, and surface interval history. Bühlmann ZHL-16C computers should produce broadly similar results, but small differences are normal. If another computer shows a significantly shorter NDL, respect the more conservative reading.

Export your dives from the Suunto app as JSON (Suunto Nautic format). In Pelagic on iPhone, go to Logbook → tap the import button → select your file. Depth profiles, tank pressure (if recorded), GPS route, and dive events are all imported.

On macOS, use File → Import Dive Log (⌘⇧I) or drag a JSON or UDDF file onto the logbook window.

Import: Suunto Nautic JSON, UDDF (Universal Dive Data Format)

Export: UDDF — compatible with Subsurface, MacDive, DiveLog, and most other dive logging applications.

PDF export of individual dives is available on macOS.

Pelagic uses iCloud to sync your logbook. Check the following:

• Both devices are signed into the same Apple ID
• iCloud Drive is enabled in Settings → [Your Name] → iCloud
• Pelagic has iCloud permission: Settings → [Your Name] → iCloud → Show All → Pelagic should be on
• Both devices have an internet connection

Sync can take a minute or two after a dive. If it still doesn't work, force-quit and reopen Pelagic on both devices.

Yes. Open any dive in the logbook and scroll to the editable fields section. You can update the site name, buddy, notes, equipment used, star rating, and gas details at any time. The depth profile and recorded sensor data cannot be changed.

On iPhone: open the dive detail, scroll to the bottom, and tap Delete Dive.

On macOS: select the dive in the logbook table and press the Delete key, or right-click and choose Delete.

Deletion is permanent and syncs across all your devices.

Yes. Apple requires explicit permission before an app can access the EN13319 depth sensor. Without it, Pelagic cannot read depth data and the dive computer will not function. Grant permission when prompted — you only need to do this once.

Apple Watch Ultra's EN13319-certified pressure sensor is accurate to ±0.1 bar, which corresponds to roughly ±1 metre depth accuracy. This meets the EN13319 standard for dive computer depth sensors.

Depth is calculated from absolute pressure minus surface pressure, sampled at ≥1Hz during the dive.

From the Surface Dashboard, press the Digital Crown or tap End Dive to stop the session. If the dive was very short (under 2 minutes), you'll be prompted whether to save or discard it.

Yes. The Watch app is fully standalone — you don't need your iPhone with you to dive. Your dive is stored on the Watch and syncs to your iPhone the next time they're in Bluetooth range.

Pelagic Pro is billed through Apple. To cancel, go to Settings → [Your Name] → Subscriptions on your iPhone, find Pelagic, and tap Cancel Subscription. You'll retain Pro access until the end of the current billing period.

Yes. The macOS app is included free with every active Pro subscription. Sign in to the macOS app with the same Apple ID and your Pro features will be unlocked automatically.

No — the macOS Standalone is a separate one-time purchase for Mac-only users. It doesn't include the iPhone Pro subscription. If you want unlimited dives on iPhone and Watch, you'll need a Pelagic Pro subscription (which also covers Mac).

Yes. All your dive data is yours and stays on your devices. After cancelling, you'll revert to the free tier (1 dive/day limit) but can still view, edit, and export your full logbook at any time.