ZH-L16C · three-point gradient factor

Three-point GF at 80 m

GF low sets the first stop, GF mid applies at the mid stop, GF high at the surface, and the GF is linear in depth between them. Each plan is compared with the straight GF low to GF high line. Change the dive below; the plans recompute in your browser.

Dive · CCR

Bottom time is runtime at the start of the ascent, descent included.

Gradient factors
GF mid, three plans

    GF by depth

    The gradient factor each plan allows at every stop on the way up, from GF low at the first stop to GF high at the surface.

    Ascent profile

    From the end of the bottom phase. The descent and bottom time are the same for all four plans.

    Stop by stop

    Stop times include the travel from the previous stop, as in a runtime table. Next to each: the GF at that stop and the change against the straight line. The mid stop row is shaded.

    How the plans are made

    • ZH-L16C tissues (compartment 1b), Schreiner equation while moving, exact loading at stops. Salt water, 10 m per bar; alveolar water vapour 0.053 bar.
    • CCR loop: diluent inert gas at ambient minus water vapour minus setpoint. Setpoint 0.70 on the descent, 1.30 at the bottom and on the ascent.
    • First stop: GF-low ceiling at the end of the bottom, rounded up to a 3 m stop, or a 6 m stop deeper than 30 m; moved one stop deeper if the ascent would already violate it (Baker's projected ascent).
    • Each stop is held to the next whole minute, then a minute at a time until the ceiling at the next stop's GF clears the next stop (Baker's stop loop). Stops every 3 m, every 6 m deeper than 30 m, last stop 3 m.
    • Rates: 20 m/min down, 6 m/min to the first stop, 3 m/min between stops and to the surface.
    • Mid stop default: halfway through the stop list. It can be fixed to any depth shallower than the first stop.

    Reading it

    Model output from an experimental algorithm. There is no empirical data behind a three-point GF. Do not plan dives from this page.

    References

    1. A. A. Bühlmann, Decompression – Decompression Sickness, Springer, 1984. ZH-L16 model and coefficients.
    2. E. C. Baker, Understanding M-values, 1998. Gradient factors.
    3. E. C. Baker, Clearing Up the Confusion About "Deep Stops", 1998.
    4. E. C. Baker, public-domain decompression programs in Fortran (stop scheduling, projected ascent).
    5. H. R. Schreiner and P. L. Kelley, "A pragmatic view of decompression", Underwater Physiology IV, 1971.
    6. libbuhlmann, open-source ZH-L16 and gradient factor library (AquaBSD, ISC licence).