Abbott FreeStyle Libre 2 User Manual page 146

Activity What You Need To Know
Sleeping
Your Sensor should not interfere with your sleep. It
is recommended that you scan your Sensor before
going to sleep and when you wake up because
your Sensor holds only 8 hours of data at a time.
For example, if you sleep for 9 hours without
scanning your Sensor, 1 hour of data will not be
collected and a gap will appear on your glucose
graph. Place your device nearby so you will receive
alarms and any reminders you have set.
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