Safety and gas bind before the survey does. Adapt to the conditions or stop — a partial ring is always a valid outcome.
Skill Session 1 is a dry, surface session — not an open-water dive. It is the planning gate the whole open-water sequence depends on: the team builds the survey plan, rehearses the pattern and the roles out of the water, and the instructor reviews and approves the plan before the first descent. A survey is a coordinated, task-loaded operation, and the time to discover that a team has no shared plan is on the surface, not at depth with a camera in hand and a gas clock running. This session exists so that everyone enters the water already holding the same plan.
It is also where the survey's arithmetic lives. The method is built so that nothing is computed underwater — the diver counts kicks and reads a compass, and every number is worked out dry, before or between dives (Appendix A). Skill Session 1 is where the team learns that arithmetic and rehearses the between-dive calculation it will perform after Dive 1.
Why dry, and why a gate. Two reasons. First, the survey loads a diver heavily — buoyancy, navigation, the camera, the count, the buddy, the gas — and a plan half-formed underwater fails under that load; planning dry removes plan-making from the task stack so that underwater the diver executes a plan already known. Second, the plan is a team product: the buddy pair and the surface support must share one mental model of the dive, and the surface is the only place to build and check that shared model. The instructor's approval is the confirmation that the model is shared and sound before anyone is committed to the water.
The Team Brief: UNITED-C
The shared mental model this session exists to build is not assembled by luck; it is built by a brief, and a good brief has a structure. This course does not invent one — it adopts an established, evidence-based framework, UNITED-C, developed by Gareth Lock of The Human Diver. UNITED-C is a sequence of seven phases, each ensuring the team has genuinely shared — not merely heard — a part of the plan before entering the water. Its job is to replace several private plans with one the whole team holds.
The seven phases map almost one-to-one onto a Reef Demographer survey:
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U — Understand the task: the objective, the hub and its reference, the ring geometry (2r-kick legs, the 000→060 heading sequence, six pictures), the calibration plan, and the definition of success — six clean captures, cleanly reconciled.
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N — Notify roles: who shoots and holds station, who records, when and how the pair swap, who leads the compass navigation.
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I — Identify resources, risks, dependencies: gas, camera, slate, and survey tools — and the day's conditions recorded on the data sheet (current, visibility, temperature) named as the threats to the dive.
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T — Test the plan: deliberately argue against the dive to find its weak points, and set the go/no-go thresholds — including the condition limits beyond which the survey is aborted or its result flagged.
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E — Establish emergency procedures: lost buddy, lost hub, gas turn-around, abort — the contingencies the slate already carries.
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D — Determine the debrief: when and where the pair will debrief, including the count reconciliation and the navigation check.
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C — Check understanding: confirm — with open questions rather than "any questions?" — that both divers genuinely hold the same plan.
Two of these phases are where the rest of this course's discipline meets the brief. The conditions the team records are exactly the input to I (naming the environmental threats) and T (setting the go/no-go on those threats) — the same "differing conditions are a caveat, not a conclusion" judgment, applied before the dive rather than after. And the instructor's approval that closes this planning gate is, in UNITED-C terms, the confirmation that C has been met: the model is genuinely shared before anyone descends.
This guide presents only the framework's skeleton and its application to the survey. The complete UNITED-C guide — the tone-setting, the red-team method, the open-versus-closed questioning, the emergency-procedure detail, and the worked examples — is The Human Diver's work, and it repays reading in full. Every student should download it, and divers serious about the human factors this framework rests on should take the training behind it.
Download the complete UNITED-C guide: thehumandiver.com/united-c
Learn the human factors behind it: The Human Diver's Human Factors in Diving training — thehumandiver.com
The UNITED-C Model © The Human Diver 2026. Presented here by reference and applied to this specialty; the framework and its complete guide are the work of Gareth Lock and The Human Diver.
The Survey Geometry on Paper
Before running the ring underwater, the team works it out on paper, so the pattern is understood, not merely followed:
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The two numbers. Every leg is 2r kicks; the survey takes six panoramas. The leg length comes from the day's visibility; the count of six is fixed (below).
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The fixed heading sequence. From the hub: swim out 000° to center 1, then add 60° at each stop — 120, 180, 240, 300, 000, 060 — a panorama at each of the six centers, the closing 060° leg returning to center 1. The team rehearses this until it is automatic, because underwater there is no table to read: the diver carries only "2r kicks, add 60°, six pictures."
The Between-Dive Calculation
The team rehearses, dry, the calculation it will perform after Dive 1:
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Dive 1 produces two kick counts: K (kick cycles over the marked 30 m / 100 ft line) and r (kick cycles to where the marker fades — the visibility radius).
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From r, the swim-out is R = 2r kicks.
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The six headings are the fixed sequence above — they are not recomputed; they are the same at every site on every dive.
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For comparison across dives, the density is expressed using r/K, so the day's kick-length cancels (Appendix A.7).
Worked through once dry, this calculation takes a minute on the surface between dives. Rehearsing it here means the team is not puzzling over arithmetic on a wet slate with a gas clock running.
Team Coordination
The roles, the unity rule, the signal set, and the gas rule are Module 6's material; this session's job is to make them this dive's plan rather than general knowledge. By the end of planning, both divers and the surface watch can state the same plan: the hub, how north is set, the heading sequence, the roles and the swap, the counted set (reef-associated organisms only), the gas plan and turn-around, and the contingencies. That shared model — not any one diver's knowledge — is what the instructor's approval confirms.
Dry Rehearsal
Before the water, the team rehearses the pattern and the roles out of the water:
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Walk the hexagon. On land or a surface platform, walk the six-station ring: out on 000°, then the +60° turns through the heading sequence, "shooting" a panorama at each of the six stops, closing the ring. Walking it makes the +60° rule and the heading sequence physical and automatic.
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Rehearse the roles. Practice the photographer/recorder hand-off and the role swap, including the capture stance and the count hand-off, so the in-water choreography is familiar before it is loaded with buoyancy and a real camera.
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Rehearse the contingencies (below), so the team's response to a problem is planned, not improvised.
Contingencies
The plan states, before the dive, what the team does when something goes wrong:
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Lost buddy contact. The standard lost-buddy procedure — search briefly, then surface to reunite — takes precedence over the survey. The ring is always abandonable; no station is worth losing buddy contact.
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Lost hub or lost count. If the hub reference or the kick count is lost, the team does not guess: the survey leg is void and re-run from the hub, or the dive is ended and the survey re-planned. A guessed station corrupts the data and is worse than no station.
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Gas turn-around. At the planned turn pressure, the survey stops where it is; the partial ring is recorded as partial. Gas always wins.
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Abort. Any diver may end the dive at any time, for any reason, without justification; the survey is always secondary to the divers.
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Exit by the hub — the radial return. When the survey is broken off out on the ring — a gas turn-around, or any abort that is not an immediate-ascent emergency — the team does not retrace the ring or press on around it; either can be the long way home. It drops the ring headings, takes the reciprocal of the hub-to-station bearing straight back to the central hub, and exits there, where the descent and ascent reference sits. One override stands above this: in a genuine out-of-gas or other immediate emergency, a direct controlled ascent with a safety stop beats swimming anywhere — ascend, do not navigate.
The Review and Approval Gate
The session ends with the instructor's review. Before approving the team for Dive 1, the instructor confirms the team can state and demonstrate:
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the survey geometry — the two numbers, why six, the heading sequence — and the between-dive calculation;
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the two roles, the role swap, and how the pair moves as a unit;
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the unity rule (no diver alone or beyond reach of a buddy), the communication signals, and the gas plan and turn-around;
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the contingencies for lost buddy, lost hub or count, gas turn-around, abort, and the radial return to the hub;
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the no-contact, no-marker, no-reel discipline and the counted set.
Approval is the confirmation that the plan is shared and sound. A team that cannot state the plan as a team is not ready for the water, and the session is extended until it can.
Performance requirements. By the end of Skill Session 1 the team will have produced a written survey plan covering site, hub, north, calibration method, the heading sequence, the two roles and the swap, the counted set, the gas plan and turn-around, and the contingencies; rehearsed the six-station pattern and the roles dry; and had the plan reviewed and approved by the instructor.
Assessment. The session is satisfactory when the buddy pair can independently state the same plan — geometry, roles, unity rule, gas, and contingencies — walk the hexagon pattern dry with the correct heading sequence, and demonstrate the photographer/recorder hand-off. The instructor's approval is required before Dive 1.