Cute Young Brunette Girl Posing In Front Of The Mirror

Signalling
With the sun as light source, a mirror can be used to signal by variations in the orientation of the mirror. The signal can be used over long distances, possibly up to 60 kilometres on a clear day. This technique was used by Native American tribes and numerous militaries to transmit information between distant outposts.
Mirrors can also be used for rescue, especially to attract the attention of search and rescue helicopters. Specialised signalling mirrors are available and are often included in military survival kits. Remember that pointing an ordinary mirror directly at the intended receiver will not work if the sun is too far off to the side. The mirror should be pointed directly between the light source and the signal target.
If there are two people, one person can hold their arm so that it points at the target. The signaler, holding the mirror as close to their eyes as possible, so as not to confuse their perspective with that of the mirror, can then see the light moving straight along the arm and directly at the target. Or if this isn't possible, improvise. A clear head in emergencies is the most essential of safety devices.