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Bühlmann Algorithm

ZH-L16 model by Dr. Albert Bühlmann — Foundation of modern dive computers

Algorithm16 compartmentsGradient Factors

⚠️ Warning — Data for informational purposes. This model underpins modern dive computers. Manual calculations do not replace a dive computer or proper training. Learn more about gas laws.

Dr. Albert A. Bühlmann (1924-1994)

Model developed at University of Zürich. Used by Suunto, Shearwater, Mares, Aqualung...

ZH-L16C

Calculation formula

P = P₀ + (Pᵢ - P₀) × (1 - e^(-t × ln2 / t½))

P₀ = initial tension, Pᵢ = inspired pressure, t = time, t½ = half-time

Understanding the Bühlmann ZH-L16 Model

The Bühlmann ZH-L16 model, developed by Dr. Albert A. Bühlmann at the University of Zürich, is the most widely used decompression algorithm in the world. It forms the computational basis of virtually all modern dive computers (Suunto, Shearwater, Garmin, Mares, Scubapro, etc.).

The 16-compartment principle

The model simulates 16 tissue compartments with half-times ranging from 4 minutes (fast tissues like blood) to 635 minutes (slow tissues like bones and cartilage). Each compartment absorbs and releases nitrogen (or helium) at a different rate. The "a" and "b" coefficients define the maximum pressure tolerated by each compartment before bubble formation.

ZH-L16A, B, and C variants

The ZH-L16A variant is the original theoretical version calculated by Bühlmann, the least conservative — generally not used as-is for diving. ZH-L16B is a modified version (lower "a" coefficients on middle compartments) intended for printed tables. ZH-L16C is slightly more conservative on several compartments and is the reference variant used in modern dive computers. Gradient Factors (GF Low/High) allow divers to adjust conservatism to their preferences.

FAQ — Bühlmann ZH-L16

What are Gradient Factors (GF)?
Gradient Factors are two values (GF Low and GF High) that adjust the conservatism of the Bühlmann model. GF Low controls the depth of the first stop (lower = deeper stop). GF High controls surface tolerance. A common setting is GF 30/85 for technical diving. GF 100/100 corresponds to the pure Bühlmann model with no additional safety margin.
How does it compare to MN90 tables?
MN90 tables are based on a 12-compartment Haldane model (SC12), different from Bühlmann. Both approaches model the same physical reality but with different parameters. In practice, Bühlmann ZH-L16C with GF around 40/85 produces profiles similar to MN90 for standard recreational dives.
Which dive computers use Bühlmann?
The majority of modern computers: Shearwater (Perdix, Teric, Peregrine), Suunto (EON, Zoop, D5), Garmin (Descent), Mares, Scubapro, Ratio. Most use ZH-L16C with customizable Gradient Factors. Only some models (e.g., Oceanic) use alternative algorithms like DSAT/RGBM.