Deep sleep tracking changes if I add more sleep

[rockpool]

Several times I have noted that the sleep curve for the whole night changes if I add more sleep later in the morning.

Last night I slept particularly badly as I was trying out a new device to minimize my snoring. 

Around four thirty I decided to remove the annoying device and get out of bed for a while. During the time I was up I checked my sleep tracking. It turned out I had actually slept for between 4 and 5 hours but had zero (!) minutes of deep sleep. Typically I get all my deep sleep, which is normally between 16 and 50 minutes, during the first hours of the night. After a while I went back to bed and managed to get all in all an extra three hours sleep (without the device this time). 

When I checked my sleep tracking next time it claimed I had 16 minutes deep sleep around 1 o'clock. My question: How could the fact that I added three hours sleep towards the end of the night increase my deep sleep several hours earlier? 

Moderator edit: format. 

[Rich_Laue]

An hour of sleep, is the minimum fitbit will detect. I've had 60 minute sleep detected. 

You can always manually add a nap, after waking up, or use the manual start/stop for shorter sleep periods. Both options will be found in the fitbit app.