Every diver's idea of a normal reef is the reef they first saw. Someone certified in 1975 and someone certified last year will both describe their first reef as ordinary, and they will be describing very different places. The change between them is invisible from inside either lifetime, because memory has no reference outside itself.
That is called shifting baseline syndrome, and there is no amount of experience that fixes it. A diver with a thousand dives has a thousand dives' worth of a reference that started in the wrong place.
The only defense is a record. Made before the change, by someone who did not yet know what would matter, in a form a stranger can still read.
That record is what you are here to make.
You arrive at this course able to measure a reef three ways. Reef Cartographer gave you its form. Reef Demographer gave you its life. Reef Hydrocaster gave you its water. Each was taught alone, and each produced its own number.
This course adds the fourth layer, the one none of them measured: the reef's appearance. What the substrate actually looks like — how much of it is live coral, how much is algae, how much is rubble, what is bleached, what is broken — photographed to a standard that lets the images be measured now and measured again by somebody else in twenty years.
Then it assembles all four into one dated document for one place, called a Site Entry, and files it in that station's Reef Site Dossier. The Dossier belongs to the site rather than to you. It may be one you open, or one somebody else opened years ago and you are adding to.
This course does not detect change, and you should not expect it to. A reef does not change measurably over the days a course takes. What you are learning is the visit — performed so the next one is comparable, documented so the next one can happen at all. The comparison belongs to whoever makes it, and one day that will probably be you, on a dive that happens long after this course ends.