Keep in mind that the wheel does not indicate exactly when you’re entering a particular stage of sleep; rather, it shows you the proportionate relationship between the stages. Also, these calculations are based on normal sleep/wake schedules and accurately reflect the concentration of stages only in people who aren’t excessively sleep-deprived. Once you’re sure that you’re in the healthy sleep zone, you can use the Nap Wheel to design and refine your nap so that it delivers the benefits most important to you.

Here’s how it works: The numbers on the outer edge of the wheel represent the 24 hours in the day. The bright blue circle represents the amount of REM sleep you’re likely to have at each hour of the day. The yellow circle represents the amount of SWS, which increases the longer you’ve been awake. Stage 2 is the constant in the equation, whether you’re napping at 2 P.M. or 2 A.M., so always figure that the first 20 minutes are almost exclusively devoted to this stage.

When you start programming your naps, the first thing you’ll do is set the “wake-up time” dial to the hour you woke up that day, say, 7 A.M. Then you’ll follow the hours clockwise until you reach your desired ratio of REM to SWS. Notice that naps occurring before 1 P.M. will have more REM (greater proportion of blue), while those taken after this time will have more SWS (greater proportion of yellow). A 90- minute nap at 1:30 P.M. is what we call the “perfect nap.”

Whether you want a pure Stage 2 nap to keep alertness high, or massive slow-wave sleep to repair your body, or extra REM for a boost in creativity or added help with memory consolidation, the Nap Wheel will let you dial up the nap that’s right for you.