I bought a mi tape the other day ~ I slept soundly during the test ~ I only slept for one night 1 ~ 3 hours! What does depth mean? straight

I tested mi band's sleep, which was really inaccurate, because one night I was lying on my side when watching the video, even counting the light sleep, which led me to sleep 10 hours that day. Actually, I only slept for six hours, so deep sleep and shallow sleep are to test whether you are still exercising at night. If you exercise, you will be counted as not sleeping, if you don't exercise, you will be counted as shallow sleep. Really sleeping in the same position. If you don't change your posture, you will fall asleep. Once you change your posture, you will enter a shallow sleep state. After a few minutes, you will fall into a deep sleep again, motionless. This is the intersection of the gray bar and the dark bar in the picture. I don't sleep well, but I sleep well. You can usually sleep for 3-4 hours. The yellow one means that I watch more videos at 7 o'clock, go to the toilet before going to bed, come back to sleep and sleep for three hours.