Heliography is the use of the sun"s light to transmit messages dating back to ancient Greek & Roman times. This is the lightest weight, highest quality signal mirror available today. It"s glass surface is encased in break-resistant acrylic, providing superior flash distance of up to 25 miles. Incredibly, this mirror actually floats! It is of course waterproof, weighs just over an ounce and has instructions for proper use on the back. Featherweight safety at an affordable price. The sighting hole features a special reflectorized screen that directs a beam of sunlight onto the target. Reflect sunlight from mirror onto a nearby surface (raft, hand etc.) Slowly bring mirror up to eye level and look through sighting hole. You will see a bright spot: this is the aim indicator. Hold mirror close to the eye and slowly turn and manipulate it so that the bright light spot is on the target.Even if no potential rescuers are in sight, continue sweeping the horizon or other possible rescuer locations, as mirror flashes can be seen for distances up to 20 miles.