Enable WebCal Address using the "Settings - Calendar" page https://rostersms.com/settings-calendar
Once you have saved the settings, a WebCal address will appear at the bottom of the page. Copy that link into Google Calendar, Outlook or Office365.
IMPORTANT: Some clients (especially Google) only refresh the calendar once per day (and sometimes slower). Therefore the calendar displayed by the Google web page does not update as fast as a normal calendar client eg. iPad or smartphone.
It also appears that Google does not update events with a start date in the past. If your pattern changes upline, it might not be updated on Google Calendar. The change is still made on the RosterSMS server. Therefore it is still better to subscribe devices directly to the RosterSMS calendar server rather than via the WebCal address.
If you need help with setting up the calendar address in Google Calendar, refer to: https://support.google.com/calendar/answer/37100?hl=en
For even more detailed help see: http://visihow.com/Use_webcal_url_to_add_a_calendar_to_google_calendar
NOTE: If you disable the WebCal Address on the "Settings - Calendar" page, then the next time you enable WebCal Address your account will have a different calendar link. This is designed to allow you to block access to your calendar after supplying the calendar link to other people.