Has any one tried those alarm clocks or phone apps that tell you when to wake up?
I would think you could figure out when you were going to be in REM with these devices (and hence the best times for WBTB) but i can't tell for sure. After all the REM cycle is approximate, right, so it would vary slightly over time.
http://www.wired.com/wiredscience/20...sleep-studies/
