use Apple Watch to track your sleep exactly!
watch app requires watchOS2.2
watch individual operation , no need iPhone
Don't use micro of iPhone, no background running.
give chart of sleep detail analysis and heart rate.
integrates with the Health app, write inbed time and asleep time data to "Health" app.Turn to health app to see the statistics.
apple watch shows result and complication.
statement:
this app can not be used for medical treatment.
1fixed watch crash bug. 2optimization algorithm
London Tube Tracker 
Dashboard for Apple Health App 