Every guide here follows the same rules: define the concept from scratch, show the arithmetic with real numbers, name the primary sources — Bühlmann, Yount & Hoffman, Erik Baker, NOAA — and back it with a free tool so you can test the idea on a real plan instead of taking our word for it. Educational only; none of it replaces training.
Measure your gas consumption properly — the number every plan is built on.
The NOAA oxygen clock and pulmonary toxicity, with a worked deco-dive example.
Work of breathing, CO₂ retention, and the 5.2 / 6.2 g/L guidance.
Equivalent narcotic depth, the O₂-narcotic convention, and choosing helium.
Setpoints, diluent choice and open-circuit bailout planning.
ppO₂ limits, maximum operating depth and equivalent air depth.
Prefer it in smaller bites? Field Notes is the same first-principles material as a daily post — on the site and on Telegram.