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Concepts

These pages explain the decompression theory and terminology AeroPlus Deco uses, so you can read the plan output meaningfully and tune the settings to match your training and physiology.

You don't need to read them in order — each page stands alone. If you're new to gradient factors, start with Gradient factors. If you're trying to understand a specific number in the output, jump straight to the relevant page.

In this section

  • Gradient factors — what GF Low and GF High control, defaults, and conservatism
  • Andy Davis method — the published method for setting GF Low on OC, and how the app's Auto-set GF Low implements it
  • Tissue saturation & GF99 — Bühlmann compartments, M-values, and reading the GF99 chart
  • TTS & deco stops — what time-to-surface means and how the runtime schedule is built
  • Gas density — the 5.2 and 6.2 g/ℓ thresholds and how helium addresses them
  • ICD & HPNS — isobaric counterdiffusion on deep gas switches, high-pressure nervous syndrome, and what the app does with each
  • CNS & OTU — central nervous system and pulmonary oxygen toxicity tracking
  • Rock bottom — minimum-gas reserve calculation and the gas plan card