Gradient factors

A gradient factor is how much of the decompression model’s allowance you are willing to use. At 100 you ascend until your tissues sit exactly on the limit the model draws, taking it raw with no margin. At 40 you stop 40 % of the way to that limit and keep the remaining 60 % as margin. DiveLogic asks for two, because the margin you want deep is not the margin you want shallow.

The two numbers

GF Low governs the deepest part of the ascent. It decides how deep your first decompression stop is. Lower it and the planner holds you deeper for longer before letting you come up.

GF High governs the surface. It decides how long the shallow stops run. Lower it and the stops at 9 m, 6 m and 3 m grow.

Between those two depths the planner slides smoothly from one to the other, so the whole ascent is governed by a gradually tightening limit rather than a single threshold. That is why the pair is written 40/70 and read as one setting: neither number means much without the other. The pair is entered as whole percentages in the Decompression section of the planner’s Plan step.

What the choice costs

Both sides below plan the same dive, 45 m for 25 minutes on 21/35, with 50 % for decompression. Only the gradient factors differ.

The conservative pair buys a deeper first stop and a longer, gentler ascent. It costs time in the water, gas, and exposure to the cold, all of which carry their own risk. There is no setting that is only better.

• GF Low moves the first stop; it does not add much time. Starting the ascent deeper changes where decompression begins more than how long it lasts.
• GF High is where the minutes are. Shallow stops are where decompression time accumulates, so lowering GF High lengthens a dive far more than lowering GF Low does.

What the pair does not tell you

A gradient factor is a fraction of one model’s allowance. It is not a probability, and GF 70 does not mean a 70 % chance of anything.

It is also not a universal conservatism dial. The factors govern Bühlmann and the Bühlmann half of both hybrid models. The Thalmann models ignore the pair completely, and the GF fields stop having any effect when one is selected. To compare a pair against a Thalmann schedule, see GF calibration.

They say nothing about the parts of a dive they do not govern either. Ascent rate between stops, gas density, cold, and how hard you worked all change outcomes without changing a single number here.

Next

• Tissue compartments describes what the factors are a fraction of.
• The first stop covers when the planner reads the ceiling GF Low draws, which decides how deep the deepest stop lands.
• Decompression settings is where the pair is set.