This preview shows page 1. Sign up to view the full content.
Unformatted text preview: tart and finish. Consequently, if you use these early dates, you may find that your performance evaluation measures are constantly showing you behind schedule. Experienced project managers usually weigh the dates produced by the scheduling system and then choose the dates they think are the most likely, given all the information that they Page 185 have at hand about the project and about the individual task. Of course, the dates they choose for the plan should be somewhere between the early dates and the late dates for each task. 7.2.2— The Critical Path If you click on either the Tracking Gantt icon at the left of the Project window or the PERT Chart icon, you will get a chart that has some of the boxes colored red. You are already familiar with the PERT Chart View from our discussion in the previous section and know that the red boxes refer to those tasks that are on the critical path , but you may not fully understand what the critical path is. To understand the concept of the critical path you must first understand the concept of float (sometimes referred to as slack or slack time). The float for a task t is the difference between the late start date and the early start date: float t = latestart t –earlystart t The float for a task is the amount of time you have to play with in scheduling the task. As long as you do not plan to start the task later than the late start date, theoretically it will not affect the completion date of the project. There are other types of float that can be calculated from the early and late start dates that are used on some projects, but we will not devote any space to them here. These other float concepts can be useful on large projects, but they are not essential. Schedulers who use these other float concepts often refer to the type of float we have just defined as total float because it is the amount of float available to a task without affecting the finish date of the total project. From a practical point of view, you would like to have large amounts of float for all tasks because the float is sort of an ''insurance" that tasks will be able to be completed in time even if unforeseen delays occur in getting the task started. However, it should be clear that it is impossible for all tasks to have a nonzero float, because then the time when the last task com - Page 186 pletes could be reduced by some time period. This would mean that the end date for the project could be shortened, which in turn would mean that the scheduling system had not really found the optimal set of dates after all. Consequently, some tasks will have floats with a time value of zero. These are the tasks that are colored red in the PERT Chart View and the Tracking Gantt View. The collection of all the tasks with zero float is called the critical path. The term path suggests that the boxes that represent the tasks on the critical path form a sequence, each box of which is connected to its successor, such that the first box in this sequence has the same start date as the project st...
View Full Document
This note was uploaded on 01/11/2011 for the course ACC 9 taught by Professor Yeetan during the Spring '10 term at Sunway University College.
- Spring '10