Editing Critical path method (section)

=== Components ===
The essential technique for using CPM<ref>Samuel L. Baker, Ph.D. [http://hspm.sph.sc.edu/COURSES/J716/CPM/CPM.html "Critical Path Method (CPM)"] {{web archive |url=https://web.archive.org/web/20100612142236/http://hspm.sph.sc.edu/COURSES/J716/CPM/CPM.html |date=June 12, 2010}} ''University of South Carolina'', Health Services Policy and Management Courses</ref><ref>{{cite book
  | last      = Armstrong-Wright, MICE
  | first     = A. T.
  | title     = Critical Path Method: Introduction and Practice
  | publisher = Longman Group LTD |location=London |date=1969 |page=5ff
  }}</ref> is to construct a model of the project that includes:
# A list of all activities required to complete the project (typically categorized within a [[work breakdown structure]])
# The time (duration) that each activity will take to complete
#The dependencies between the activities
# Logical end points such as milestones or [[deliverable]] items

Using these values, CPM calculates the [[longest path]] of planned activities to logical end points or to the end of the project, and the earliest and latest that each activity can start and finish without making the project longer. This process determines which activities are "critical" (i.e., on the longest path) and which have no float/slack or "total float" zero (i.e., can not be delayed without making the project longer). In project management, a critical path is the sequence of project network activities that adds<!-- sequence is singular --> up to the longest overall duration, regardless of whether that longest duration has float or not. This determines the shortest time possible to complete the project. "Total float" (unused time) can occur within the critical path. For example, if a project is testing a solar panel and [[Task (project management)|task]] 'B' requires 'sunrise', a scheduling constraint on the testing activity could be that it would not start until the scheduled time for sunrise. This might insert dead time (total float) into the schedule on the activities on that path prior to the sunrise due to needing to wait for this event. This path, with the constraint-generated total float, would actually make the path longer, with total float being part of the shortest possible duration for the overall project. In other words, individual tasks on the critical path prior to the constraint might be able to be delayed without elongating the critical path; this is the total float of that task, but the time added to the project duration by the constraint is actually [[critical path drag]], the amount by which the project's duration is extended by each critical path activity and constraint.

A project can have several, parallel, near-critical paths, and some or all of the tasks could have free float and/or total float. An additional parallel path through the network with the total durations shorter than the critical path is called a subcritical or noncritical path. Activities on subcritical paths have no drag, as they are not extending the project's duration.

CPM analysis tools allow a user to select a logical end point in a project and quickly identify its longest series of dependent activities (its longest path). These tools can display the critical path (and near-critical path activities if desired) as a cascading waterfall that flows from the project's start (or current status date) to the selected logical end point.