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For more information about the Calendar iCal see Calendar iCal
Add a Google Calendar
Login to your Google Calendar account
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In the Calendar Details screen look for "Private Address". Notice that it has an ICAL logo.
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Click the ICAL button.
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Copy the ical link (don't click it as that will just download the file). Now go to the calendar module. Click "Add Remote iCal Calendar"
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Name: The name of the calendar
Description: The description of the calendar
Remote URL: The ical link you copied from above
Synchronization Time: How often to sync the remote Google calendar with the local calendar
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