How do I restrict view of other colleagues' calendars by business role?

Hello Gurus

I need to allow the area sales manager to view the calendars of his sales managers but I must prevent the sales managers from viewing the calendars of other sales managers in the organistion.

At the moment it appears there is no role specific authorisation and I can view any of my colleagues calanders. Please advise how I can implement this?

Regards

Declan