Gradient Factors

A pair of percentages, like GF 30/70, that scale the Buhlmann algorithm's tolerated tissue overpressure to add conservatism to a dive plan.

Gradient factors are the standard way to tune conservatism in a Buhlmann based dive computer. They are expressed as a pair of percentages, such as GF 30/70: GF low sets what fraction of the maximum tolerated tissue overpressure, the M-value, the model allows at the first stop, and GF high sets the fraction allowed when surfacing. GF 100/100 would ride the raw ZHL-16 limits with no safety margin.

A lower GF low pushes the first decompression stop deeper, an idea inherited from bubble model thinking, while a lower GF high lengthens the shallow stops and surfaces you with less supersaturation. Recent decompression research has shifted opinion away from very deep first stops, so many technical divers now run settings like 50/80 rather than the once popular 20/85 style profiles. Recreational computers often hide the same machinery behind labeled conservatism levels.

Whatever pair you choose, know what your computer is actually running, since two divers on the same dive with different gradient factors will see different ceilings and stop times, which matters for team planning. Changing GF mid trip also changes how residual loading is interpreted, so pick settings you understand, stay consistent across a series of repetitive dives, and adjust deliberately rather than reactively.