Critical Path — Technical Terms
Before explaining how to calculate a Critical Path, some common technical terms need explaining :
Activity
A distinct item of work completion of which is necessary to finish the project.
Duration
A realistic, best estimate of the amount of time necessary for accomplishing the work involved in an activity. Measured in time units. eg days.
Early Start (ES)
The earliest point in time when an activity can start, assuming all prerequisite activities take place as scheduled.
Early Finish (EF)
The earliest date that an activity can finish, assuming that it began on its early start date.
Late Start (LS)
The point in time by which an activity must start if there is to be no delay in subsequent activities.
Late Finish (LF)
The date by which all work involved in an activity must be completed in order to avoid delaying subsequent activities.
Critical Path
The sequence of activities from project start to finish that has the least amount of float, i.e., requires the longest total amount of time to complete.
Longest Path
The longest path refers to the sequence of activities with the highest total duration. It may or may not be the critical path.
Total Float
The amount of extra time available to an activity or activities on a path when all activities start as early as possible.
Free float
Uniquely available to an activity. It also indicates the duration that the activity can be delayed without delaying successor tasks
Slack
Another term used for Float
Task
Another term for an activity
Zero float
Denotes activities that have no flexibility but must start and finish on or before their scheduled dates for the project to be completed on time.
Negative float
Denotes activities scheduled to occur after their late dates. The project is delayed.