“Free-Busy Sharing”: which displays free and busy time blocks only, with no
details regarding Subject, Attendees, etc.
“Read-Only Sharing”, which displays both free/busy time and event details,
but does not permit changes to event dates, times, or details.
“Full Sharing”, or Administrative Access, which allows users to not only view
your calendar, but also provides the ability to add and edit appointments.
Note: Users of other Calendar systems can only have Free-Busy Sharing