Empty or no batteries at all inside the strobe or camera, no memory card in camera, hot-shoe not connected, housing buttons not lined up, auto-focus not switched on, lens-cap still on camera, etc. – Every single one of these minor problems can quickly turn into a big frustration underwater, because you’re not able to fix it without opening the housing! Eliminate all that by simply taking a test shot after setting up your camera equipment and before going diving. Make it a habit to take a test shot of your lens-cap and you will instantly see if everything is working fine – if not, you’re still able to fix it before you go diving!