What gradient factors actually do
Posted 08 June 2026 · Field Note #1
Gradient factors, in plain English
Think of decompression as climbing out of a pressurised world. While you're deep, your body quietly soaks up inert gas, mostly nitrogen, into its tissues. Surface too fast and that gas fizzes out as bubbles, like a shaken bottle of soda. The whole job of a decompression model is to tell you how slowly to climb so the gas leaves gently, through your lungs, instead of forming bubbles.
The Bühlmann model draws a hard ceiling for each tissue, the so-called M-value: the most a tissue's gas pressure may exceed the pressure around you before bubbling becomes likely. Riding that raw ceiling is aggressive. Gradient factors are simply two safety dials that let you stay a chosen percentage below that limit.
GF-low is the first dial. It decides how deep your first stop appears. A lower number forces that stop deeper and slows your ascent off the bottom. GF-high is the second dial. It governs how much supersaturation you'll accept when you finally surface. A lower GF-high buys more shallow-stop time and a gentler finish.
Why does this matter physically? Gas leaves your tissues fastest when there's a big pressure gradient between the gas dissolved in you and the gas around you, but push that gradient too hard and you cross into bubble territory. Gradient factors let you decide, deliberately, how much of that allowable gradient you're willing to spend.
Practically: there's no universally correct pair. Most recreational and technical divers settle somewhere in between, with settings like 40/85 being common. On a cold, hard, or tired day, tighten GF-high to pad your shallow stops. If you want a more gradual departure from the bottom, drop GF-low. Remember they change only how cautiously you off-gas, never the gas in your tanks.
Pick your numbers on the surface, with clear hands and a clear head, and know exactly what you traded away.
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⚠ Educational only — not a substitute for training or a dive computer. Verify every number independently and dive within your certification.