Four reference charts, toward the corners of the frame, labeled A to D clockwise. The frame's long side runs along the bearing to the photo point, and A is the far-left corner when you face along that bearing. Their known size gives the scale, for you now and for anyone who opens the image in fifty years. And because four charts of the same size appear the same size only when the camera is square to their plane, they are also a spirit level you can see.
The white and gray panels on those charts give the exposure reference. The white panel matters more than it sounds. Bleached tissue is white; a clipped highlight is also white; so a frame shot a stop too bright will manufacture bleaching that was never there, and the resulting photograph will look perfectly fine. The white panel is what catches that: if it is clipped, the frame is not used.
That is all that goes in the frame. No color card, no health chart. The Coral Health Chart does its work in the water, in your hand, against the colony — which is what it was made for — and that survey is where the station's condition record lives.