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Typically, all calendar applications require a URL for the calendar you want to subscribe to.

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Copy this entire URL and follow the instructions for your calendar application for 

• Google Calendar
• MacOS Calendar - How to subscribe to calendars in MacOS Calendar
• iOS devices (iPhone / iPad), However, an easier method is to email the calendar URL to your iOS device and in iOS Mail, click on the calendar URL. You will be prompted if you want to subscribe to the calendar.
  
  • An useful iOS calendar app is Calendars 5 by Readdle which syncs with local iOS and Google Calendars. It costs $6.99 US and comes with iPhone and iPad versions.
• Windows 8 desktop and Windows 8 devices, check out the OneCalendar application. See related GigaOM article.
• Windows 10 users, learn how to setup the default Windows 10 calendar app which works with Google Calendar, Apple iCal and Microsoft Outlook
• Sync Android devices (phones/tablets) with Google Calendar. You first must subscribe to the At-Large Calendar using Google Calendar , then sync your Google Calendars with your Android device.
  • Some Android calendar apps :  Google Calendar (from Google, free) ; Sunrise (free) ; DigiCal 
• Microsoft Outlook (Internet Calendar Subscriptions)
• Outlook.com (under "Subscribing to a calendar")Yahoo! Calendar
• Mozilla Lightning (extension for Mozilla Thunderbird)

on how to subscribe to the At-Large calendar by URL. 

Screenshot of At-Large Calendar