Are you averaging more good or bad sleep? Short or long?
Record wake up times and fell asleep times on the Birdhouse web app and rate how it went, or just use mobile and it'll still give you durations.
* Sleep durations requires a Birdhouse Premium membership
To review and discover:
Go to Reports > Select a date period > select Sleep > select Advanced Filters > Select Woke Up, see the ratings and durations charts!