All of the above
hazardous marine life
Have them inspected and serviced annually by a qualified technician.
Do not subject them to extreme temperature changes.
overpressure relief valve
remove the flag when divers are not in the water
fly from your surface support station
there are laws in parts to the world that require you to log dives
dive operators may review your logbook before they will provide services
spare parts kit
use your buddy’s shoulder for support
an item of gear needs adjusted
if your scuba unit gets caught in fishing line
sun brightness/available light