Measuring sleep

One of the things I like about my Fitbit is that it measures my sleep. I try to get a good night's sleep... usually between seven and eight hours. Like a lot of people, I do not sleep that well. I toss and turn. I wake up groggy, look at the clock and try to go back to la la land.
The Fitbit gives me a chart every morning, telling me how much time I slept and whether it was light sleep or deep sleep or restlessness.
So last night I hit the bed at 11:41 p.m. and got up at 8:48 a.m. But when all the time was counted, it only came to 7 hours and 25 minutes. (Click on the chart to make it full size.)

My light sleep was more than five hours. The deep sleep was just over one hour.
Interestingly, a couple of weeks ago, the Fitbit recorded a nap I had on the weekend. I hit the couch and was restless for about seven minutes and then went into a deep sleep for more than an hour. All that from napping on the couch. I should nap more often :)