Today, we’ll be shedding light on another such aspect – slack time. We have explained several such concepts such as project management crash or budget in project management. But planning also helps in keeping the variables in check so that there are not any last-minute surprises that could delay the project, or worse, lead to project failure. For example, if a piece of key equipment is only available for a few days, activities that depend on it have the same start and finish dates in the forward and backward passes.When it comes to project planning, we think it’s important because it helps us to execute the project better, right from ideation to completion. The difference between the early start date and the late start date for activities on the critical path is usually the same as the total float, unless the activities are affected by the resource calendars differently in the forward and backward pass. Assign the calculated date as the late start date of the predecessor activity.Refer to the resource calendar(s) that applies to the people and equipment necessary for the activity, and subtract the number of off days that the activity would span on those calendars. Subtract the lag time or add the lead time to the late finish date.Subtract the predecessor activity’s duration from its late finish date.Follow these steps to calculate the late start dates of predecessor activities, assuming finish-start relationships: To calculate late start dates, begin with the project completion milestone and assign that date as the finish date of its predecessor activities. Resource calendars must be considered in the backward pass as well as the forward pass. Subtract the duration of each activity in each path to determine the latest date the activity could begin and still meet the project completion date. The next step is to work through the network diagram from right to left beginning with the mandated completion date, which is a milestone that is set in the project plan. The float on those activities is called free float. If activities that are not on the critical path have a difference between their early start date and their late start date, those activities can be delayed without affecting the project completion date. A project can also have negative float, which means the calculated completion date of the last activity is later than the targeted completion date established at the beginning of the project. Any delay in an activity on the critical path would reduce the amount of total float available on the project. Total float is the difference between the finish date of the last activity on the critical path and the project completion date. Floatįloat, sometimes called Slack (float), is the amount of time an activity, network path, or project can be delayed from the early start without changing the completion date of the project. Computer software must be combined with common sense or good judgment. Fortunately, there are computer programs to assist in the process, but the project manager must understand the process well enough to recognize computer errors. Assign the calculated date as the early start date of the successor activity.ĭoing this process manually is error prone and time consuming.Refer to the resource calendar(s) that applies to the people and equipment necessary for the activity, and add the number of off-days that the activity would span on those calendars.Add the lag time or subtract the lead time.Add the predecessor activity’s duration to its start date.Follow these steps to calculate the early start dates of subsequent activities, assuming finish-start relationships: To calculate early start dates, begin with the project start date and assign that date as the start date of activities that have no predecessor activities. The estimate considers durations and resource availability calendars. The early start date for an activity is the earliest date the activity can begin. The dates derived by this method are the early start (ES) dates. Starting dates can be assigned to each activity by doing a forward pass proceeding from left to right in the network diagram beginning with the project start date.
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