Safety and gas bind before the survey does. Adapt to the conditions or stop — a partial ring is always a valid outcome.
Dive 4 is the assessment. The student runs the entire method alone; the instructor observes and intervenes only for safety, never to instruct. Everything the course has built is exercised in one dive: re-locate the hub, set north, calibrate the day (K, r), derive R = 2r and the six headings, run the six-station ring with the two-observer count, and compute the site index topside. Where Dive 3 taught re-occupation with the instructor's hand on the process, Dive 4 removes that hand — the card the student earns says they can do this unsupervised, and this is the dive that proves it.
The dive re-occupies the same hub as Dives 2 and 3. This keeps the assessment focused on execution rather than on finding a new site, adds a third full-radius reading to the hub's record (tightening the noise-floor estimate), and sets up the optional half-radius diagnostic check of Dive 5 at a hub whose full-radius behavior is now well characterized. (An instructor who wants to test site-independent setup may instead assign a fresh hub; the trade is that the optional Dive 5 check, if run, then has only this single survey to compare against, rather than a measured noise floor.)
What "independent" means here. The student leads every step: the descent and hub re-location, setting and confirming north, the calibration swim and the reading of K and r, the derivation of R = 2r, the navigation of all six legs, the camera work and station-keeping, and the management of the buddy and the gas plan. The instructor's role is reduced to safety supervision and post-dive verification. Prompting the student through a step they have forgotten converts the dive from an assessment into instruction, and the performance requirement is not met.
Performance requirements. By the end of this dive the student will have, without instructional prompting:
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Re-located the hub and re-established north independently.
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Calibrated the day (K, r) and derived R = 2r and the six headings independently.
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Run the complete six-station ring (out 2r on 000°, then the +60° edge headings), a panorama at each center.
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Produced a reconcilable two-observer count of reef-associated organisms.
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Computed the six densities and the site index D̄, and added the reading to the hub's record.
Equipment for this dive. As Dives 2 and 3.
Pre-dive briefing. The briefing is led by the student, who states the plan: the hub, how north is set, the calibration method, the heading sequence, the two-observer roles, the counted set, and the gas plan. The instructor confirms the safety plan but does not supply the survey procedure — the student must already hold it. Confirm the no-contact, no-marker, no-reel discipline.
The dive. The student executes the full survey — calibration, the six-station ring, the two-observer count — exactly as in Dives 2 and 3, leading throughout. The instructor observes position, buoyancy, navigation, and team conduct for the assessment, intervening only on a safety matter.
Post-dive. The student offloads, reconciles the counts, computes the six densities and the site index, and adds this third full-radius reading to the hub's record. With three full-radius readings now in hand (Dives 2, 3, and 4), the hub's baseline mean and its spread are better established — the more readings on unchanged structure, the more confident the noise floor. Debrief the student's independent performance against the requirements.
Assessment. The dive is satisfactory when the student has run the complete method from hub re-location to computed index with no instructional prompting, produced reconcilable counts and a defensible site index, and conducted the dive with sound buoyancy, navigation, gas management, and team procedure. A dive that required prompting through a survey step is repeated; a safety intervention by the instructor ends the assessment.
Depth range. 6–13.5 m / 20–45 ft (Day 2), consistent with the gas plan.