Linking Tasks, Buffers and Lag Time
Cheryl Wetherington -
Article & Video: Linking, Buffers, and Lag
Linking Tasks Together
When you link tasks together, you create a dependency between them. The most common linking type is "Finish to Start" linking. On the Gantt chart, you will see both tasks with a link line connecting them:
This type of link indicates the second Task (the Successor) cannot begin until the first Task (the Predecessor) has been completed. If the Predecessor Task is moved, the Successor Task moves as well, and maintains its relative position to the Predecessor.
To link tasks together this way, simply select the checkboxes next to the tasks then click on the icon on the toolbar.
You can also link tasks "Start to Start" (e.g. both tasks must start on the same date):
or "Finish to Finish" (e.g. both tasks need to finish on the same day):
To link tasks together in this way, click on the "Links" menu then choose the appropriate link option.
Buffers and Lag Times
A buffer is designed to allow a task to overrun without impacting the rest of the schedule. If a task is extended in duration then it can eat into the buffer (increase duration and decrease buffer) without affecting the overall timeline. In the example below, Task A has a Buffer of 2 days. You also see this buffer reflected on the Gantt chart as the tan portion of the Task’s bar.
To create a Buffer on a task:
- Create a new task or
- Select the checkbox next to the Task; click File and then Edit Task
- In the New Task or Edit Task dialog, click on the "Advanced" tab
- Enter a value in the Buffer field and click OK
Alternately, you can add the "Buffer" column to the Task list and add values using in-line editing.
Note: Once a task is complete then it no longer needs a buffer. Consequently, when you mark the task 100% complete, the buffer disappears. Once the Predecessor Task is marked complete, if you have any tasks linked to the this task, the Successor Task's date will move as soon as the Predecessor is marked complete.
Lag Time is a waiting period between the end of one task and the beginning of another. For example, Task A ends on May 30 but Task B has to start two days after Task A is completed. In this case, you will want a Lag Time that spans 2 days.
To create a lag between tasks:
- Link the tasks together using Finish to Start linking.
- Change the Start Date on the Successor task (Task B in the example above). You can change the date using the Start field in the task list or you can drag and drop the task on the Gantt chart.
If the Predecessor task (Task A in the example above) is moved, it will force the Successor task to move but the lag time will remain intact. When you mark Task A complete, the lag time will also remain intact.
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