ATracker can read the user calendar and show it in the "Calendar" and "History" tabs.
The device will ask permission to access the calendar when the user enables this setting for the first time.
ATracker will let the user pick which calendar/calendars the user wants ATracker to display in the "Calendar" and "History" tabs.
In some cases, after an iOS update or device restoration, the user might need to disable the calendar read and enable it again to reauthorize access.
For iOS users, please also check iOS->settings->privilege on whether ATracker can access the calendar. By default, it is allowed after the user grants the permission.