Resources by definition are constrained. A person works only so many hours per day. A person also has a defined set of non-work times such as weekends and holidays. Likewise, equipment may be available only at certain times. In the prior section on Resources, we mentioned that a resource can be associated with a calendar. Let us now discuss the definition and use of calendars.
Calendars describe the time available for project work. A calendar can be defined at three levels: global, project, and resource. A resource calendar is designed to work for a specific resource. Furthermore, calendars can be assigned to activities and to the resources assigned to that activity.