A Common request from users is to grant others access to their calendars. You can either talk the user through this, or setup a new outlook profile to open their mailbox and set it yourself using the GUI – both are time consuming. This simple powershell command allows you to set permissions with ease:

add-mailboxfolderpermission -identity USERNAME:\calendar -user “Username of person who needs access” -accessrights reviewer

or users with a Dutch language mailbox:
add-mailboxfolderpermission -identity USERNAME:\agenda -user “Username of person who needs access” -accessrights reviewer