# Fathomline — Scuba dive log & study guide > Scuba dive log & study guide (iPhone/iPad app by Robert Corbin.) - Source: https://appshunter.io/ios/app/fathomline/id6777667619 (this page in markdown: same URL + `.md`) - Developer: [Robert Corbin](https://appshunter.io/developer/1890247992) - Category: Sports, Lifestyle - Price: $0.99 (on sale, was $1.99) - Age rating: 4+ - Requires: iOS 17.0 · 4 MB - Languages: English - Released: 2026-06-10 - Data updated: 2026-08-09 - User reviews in markdown: https://appshunter.io/ios/app/fathomline/id6777667619/reviews.md ## What is Fathomline? Fathomline is a beautiful, private dive logbook and study companion that works completely offline. No account, no subscription, no ads - buy it once and your dives stay on your phone, forever. Whether you're a new Open Water diver building your first pages or a divemaster with hundreds of dives, Fathomline keeps your logbook fast, gorgeous and yours. LOG EVERY DIVE • Site, location, dive type, water and conditions • Max and average depth, bottom time, water and air temperature, visibility and current • Gas mix (air or nitrox), cylinder, start/end pressure and weighting • Buddy, dive centre, a 5-star rating, tags and free-form notes • Carry over a paper-log total so your grand total is always right KNOW YOUR NUMBERS • Automatic SAC and RMV (your true breathing rate) for every dive with two pressures • A clean Stats screen: totals, deepest, longest, distinct sites and countries • Depth distribution, dives by year, dive-type breakdown and your top sites • An RMV trend chart so you can watch your gas efficiency improve OFFLINE STUDY TOOLS • Nitrox calculator: MOD, EAD, best mix and ppO₂ at any depth, plus a full EAN21–EAN40 reference table • Gas-planning aids: rule of thirds, half-plus-reserve turn pressure and a runtime estimate • Unit converter for depth, pressure, temperature and gas volume • Switch the whole app between metric and imperial any time A POCKET DIVE LIBRARY • 50+ marine-life ID cards - what it is, how to identify it, and how to behave around it • 140+ term dive glossary, from "bottom time" to "thermocline" • 30+ underwater hand signals grouped by purpose • Skills & drills refreshers, dive-type guides and equipment-care schedules • Plain-English safety and best-practice summaries YOUR DATA, YOUR DEVICE • 100% offline - works in airplane mode, on the boat, anywhere • No account, no login, no cloud, no tracking, nothing leaves your phone • Export your whole logbook as a text report or CSV spreadsheet whenever you like • One-time purchase, every feature included Fathomline is a personal logbook and educational reference - not a dive planner, dive computer, or decompression tool. Always dive within your training and certification, use a dive computer and/or tables, plan conservatively, and follow your certifying agency's guidelines. Dive safe. Log beautifully. Keep your data. ## Version history (last 4 releases) ### 2.0.1 — 2026-06-25 This update sharpens the interface: the iPad layout now uses a centered, comfortable reading width instead of stretching edge to edge, so every screen reads as a clean column. iPhone is unchanged; still fully on-device. ### 1.2 — 2026-06-15 Version 1.2 - two substantive new features: CNS OXYGEN TRACKER Every applicable dive now shows an estimated CNS % on the dive detail screen, calculated from the NOAA single-exposure table (the same table used in every Enriched Air course). See your ppO2 at working depth, the NOAA time limit for that gas, and how close you are to the 80 % single-dive working limit. CNS exposure is shown for nitrox dives and for deep air dives that reach the table range (ppO2 0.6 bar and above). The Tools tab adds a full interactive CNS calculator - enter any gas and depth to get the exposure estimate and the complete NOAA reference table at a glance. The Stats screen shows your total accumulated CNS % across all logged dives where a CNS reading applies. MILESTONES A new Milestones card on the Stats screen tracks six categories of personal achievements: total dives (10, 25, 50, 100, 200, 500, 1000), cumulative bottom time (10, 25, 50, 100, 250 hours), depth reached (18, 30, 40 m), distinct sites visited, nitrox dives, and night dives. Each earned milestone shows a gold checkmark; upcoming milestones show a progress bar so you always know how close you are. All new features are fully offline. CNS tracking is clearly presented as an educational reference - not a real-time dive computer. ### 1.1 — 2026-06-14 Version 1.1 — three substantial new features, all fully offline: REPETITIVE DIVE PLANNER An interactive PADI RDP reference built into the Tools tab. Enter your first dive (depth + time) to see your exit pressure group, then dial in your surface interval to find your new group, and plan your next dive with the correct adjusted no-decompression limit (ANDL) and residual nitrogen time (RNT). Includes an NDL quick-reference table for all recreational depths. Always shown with a clear training disclaimer — this is an educational study aid, not a dive computer. SITE NOTEBOOK A personal notebook for dive sites you return to. Store typical depth, visibility, water temperature, a star rating, and your own notes. Linked to your logged dives at that site — tap any entry in the notebook to see your full dive history there. Access from the Logbook tab (top-left mappin icon). PDF LOGBOOK EXPORT Export your entire dive logbook as a formatted PDF — diver profile, summary statistics, a full dive table and a diver/instructor signature block. Perfect for showing a liveaboard, dive shop, or course instructor your experience at a glance. Find it in Settings → Your data → Export PDF logbook. ### 1.0 — 2026-06-10 No release notes. ## More apps by Robert Corbin - [Daily Word Journey](https://appshunter.io/ios/app/daily-word-journey/id6761548266) - [Hush Secret Text](https://appshunter.io/ios/app/hush-secret-text/id6761658175) - [Renew Guard](https://appshunter.io/ios/app/renew-guard/id6761755447) - [Receipt to PDF](https://appshunter.io/ios/app/receipt-to-pdf/id6761782025) - [Route Your Pay](https://appshunter.io/ios/app/route-your-pay/id6761783719) - [Tip Arbiter](https://appshunter.io/ios/app/tip-arbiter/id6761786879) All apps by Robert Corbin: https://appshunter.io/developer/1890247992 --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-08-09.*