Decompression Algorithm

The mathematical model a dive computer uses to track inert gas in the body and compute no-deco limits and stops, such as Buhlmann ZHL-16 or VPM.

A decompression algorithm is the mathematical model a dive computer or planning tool uses to estimate how inert gas loads and leaves your body, and therefore how long you can stay, how fast you can ascend, and what stops you owe. The most widespread is the Buhlmann ZHL-16 family, a dissolved gas model that tracks 16 theoretical tissue compartments with nitrogen half times from about 4 to 635 minutes and limits each one against a maximum tolerated overpressure, its M-value.

Bubble models take a different view: VPM, the Varying Permeability Model, assumes microscopic bubble seeds always exist and shapes the ascent to keep them from growing, which historically produced deeper first stops. In practice, modern implementations converge, and Buhlmann with gradient factors has become the de facto standard in technical diving computers, letting divers dial conservatism onto the raw model.

No algorithm measures your body directly. All of them are statistical maps of risk fitted to trial data and field experience, which is why identical dives can feel different day to day and why the same profile can bend one diver and leave another untouched. Padding conservatism when you are cold, tired, dehydrated, or diving repetitively is sound practice no matter which model runs on your wrist.