...expand underwater vision while staying in a streamlined horizontal position to efficiently move through the water.

...save the air/gas normally used to constantly shift your body and equipment to see beyond your mask view.

...inspect tank valves and hose connections to check for gas leaks. Quickly see the size and location of a leak.

...avoid surfacing to fix a problem. See and fix it yourself while underwater and then enjoy your dive.

...shut down the correct side of a doubles manifold with no guesswork in the event of a leak.

...find the location of a dry suit leak while underwater.

...check rebreathers for leaks.

...check for clearance above your tanks while diving in a wreck or cave.

...monitor divers behind you in the passageway of a wreck or cave.

...make sure you are not kicking silt or coral with your fins.

...make safe controlled ascents. Watch your gage and use the mirror to see above.

...spot divers above you on a crowded line while simultaneously monitoring your gauges.

...avoid having water trickle into your drysuit neck seal as a result of looking up.

...scan the ceiling of a cave for fossils without looking up.

...track sea life in two places,for example, visually track a shark overhead while observing a ray on the bottom.

...locate a dive buddy that ends up above or behind you. No need to twist around to find them.

...do a surface swim on your back without stopping to turn and look for the marker.

...escape from entanglements.See what you are caught on and calmly detach yourself.

...easily see around if your movement is even more limited by a physical disability.

...keep an extra eye on your students during underwater training exercises.

...find equipment that ends up caught behind you. Relax and find it in your mirror.

...sight down the length of your body to check for a streamlined configuration.

...observe the reaction of sea creatures when seeing their own reflection.

...redirect sunlight to see underneath ledges and into shadows.

...signal rescuers at the surface in an emergency. The flash from a mirror can be seen for many miles.

...find and replace a contact lens.

...inspect your mask seal before entering the water.

...check your face after the dive for...

...avoid having a mischievous diver sneak up on you.