Hi
to overlay calendars and create a global one, you need to follow these simple steps:
- In Calendar List, go to the Calendar tab and click Calendars Overlay to open the Settings for Calendar Overlay:
- In Calendar Overlay Settings, click New Calendar to add a new Calendar
- To setup your new calendar, begin by selecting a name for the Task List or other Calendar List for the new calendar. Next, you will need to input some information about your new calendar. This includes the color which you would like assigned to the item in calendar view; the Web URL for your list, and the list type.
- Follow the above steps to create multiple calendars for your Calendar Overlay. Please note that SharePoint allows a maximum of 10 calendars per view in Calendar Overlay.
- Show data from many Lists in a Calendar View of a Calendar List:
- After you have added all your calendars into the Calendar Overlay, you can view all of the data from the calendar overlay in a single calendar view:
SharePoint and Office 365 : How to ?? 