In development — course content is not for public use pending PADI approval.
Census Tools

Confirmed counts in, census metrics out

These calculators turn your human-confirmed field data into the census metrics — all in your browser, no login, no data sent anywhere, and they keep working offline once the page has loaded. The arithmetic is exactly what the course guide specifies; nothing here replaces your judgment about what the numbers mean.

Each capture's density is its count over the disk it sampled, D = N / (π r²), expressed through the ratio r / K so the day's kick-length cancels and dives compare. The site index is the average of the six D̄ = mean of Dᵢ — densities averaged, never counts pooled.

Field data

From the slate: the day's calibration and the six confirmed counts.
The count of record is the human-confirmed image count; report it with the two-observer spread (the in-water tally vs. the image count), never as a bare number. Densities are in organisms per m² of reef surface, for reef-associated life only.

Re-occupy a hub on unchanged structure and the reading still moves a little. That spread is the noise floor — the smallest change the survey can trust. A later reading counts as real change only if it moves by more than the floor.

Repeat readings

Site indices D̄ from re-occupations of one hub on unchanged structure (Dives 2, 3, 4…).
The floor here is the full spread (range) of the repeat readings — the honest, conservative yardstick, since it bundles counting, sampling, navigation, and short-term biological variation together. The standard deviation is shown too once you have three or more readings.

From the species tally: richness, the abundance-weighted diversity indices as effective numbers of species exp(H′) and 1/λ, Pielou evenness J, and the unified Hill profile at q = 0, 1, 2.

Species tally

One row per species, with its total count across the hub.
Species (optional)Count
The course leads with the abundance-weighted indices (Shannon, inverse-Simpson) because they are robust to the survey's blind spot. Richness is indicative only — the small, cryptic species it depends on are exactly the ones a diver most often misses, so it is roughly three times as sensitive to that bias.

How much the community's composition moved between two visits. Bray–Curtis weighs abundances; Jaccard weighs only presence and absence. Both run 0 (identical) to 1 (nothing shared) — the compositional analog of the noise floor.

Two visits

One row per species, with its count at each visit (0 if absent).
Species (optional)Visit AVisit B
Turnover detects what density cannot — a hub can hold D̄ flat while one aggressive species replaces ten. Judge it against the turnover you get re-occupying unchanged structure: real community change is what exceeds that.

The relative rate of change in abundance between two readings a time apart: r = ln(D̄ₜ / D̄ₜ₋₁) / Δt. Like everything here it is a rate of change of the index, honest about the index's own limits.

Two readings

Site indices D̄ at an earlier and a later visit, and the time between them.
A positive rate means the index rose; negative means it fell. Whether the change is real is still judged against the hub's noise floor — a rate inside the floor is not distinguishable from method noise.

Assemble everything you've entered and calculated into a clean census report — including the guide's accuracy-and-limitations statement — then use your browser's print dialog to save it as a PDF or send it to a printer.