The power nap is thought to maximize the benefits of sleep versus time. It is used to supplement normal sleep, especially when a sleeper has accumulated a sleep deficit.
The short duration of a power nap is designed to prevent nappers from sleeping so long that they enter a normal sleep cycle without being able to complete it. Power naps restore wakefulness and promote performance and learning.
see link: "http://en.wikipedia.org/wiki/Power_nap"
Power Nap is easy to use.
1- Setup maximal nap duration.
2- Put the device in your hand and start to sleep.
3- If the device fall down, you are in the deep sleep.
4- It's time to wake up.
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just for fun :
Power Nap - Music Video https://www.youtube.com/watch?v=KgphH2Y2XFo
picture by Bryon Lippincott