If your kit is held together with duct tape, remember that the tape might not last the whole trip. If it comes undone it may make its way to your dome port. If you are as quick thinking as I am, it will only take 4-5 shots before you realize what's wrong with your shots.

Now, once you have removed the tape from the dome port and stuffed it somewhere, it may take you a couple of dives to notice the adhesive residue. Once you've downloaded the card to your laptop and you notice these strange aberations on all of the images, it may finally occur to you to check the port. Once this was done, I took my ear juice and rubbed off the adhesive from the dome port.
On a positive note, the duct tape may actually substitute for a gray card if not too shiny.
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