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Precedence Diagrams

The process of identifying and documenting specific tasks which has to be done in order to accomplish a number of project objectives is critical. Therefore a proper project management is vital and this involves accurate activity sequencing. Some of the methods used include such as Arrow Diagramming Method, Precedence Diagramming Method, Network Templates, and Conditional Diagramming Methods. Precedence Diagramming Method is also referred to as Activity On Node method.

In this method, there are for categories of logical relationships and includes: Finish to Start –whereby previous activity has to be completed before any subsequent work can be commenced; Finish to Finish –whereby previous activity has to be completed before subsequent work is completed; Start to Start –whereby previous activity has to start before subsequent work activity is initiated; Start to Finish –whereby previous activity has to start before subsequent activity is completed (Render & Stair, 1982).

In the Precedence Diagramming Method, dummy links are unnecessary to display the logic correctly and besides it is used to execute the Forward Pass, Backward Pass, and Slack/Float calculations. It does this by applying a method known as Critical Path Method (CPM). Critical Path Method refers to a technique applied in network analysis to precisely predict the duration a particular project may take to complete. It does this by ‘analyzing the path that has the least amount of scheduling flexibility’.

Thus, early dates are calculated by using Forward Pass whereas late dates are calculated using Backward Pass. Subsequently, Forward Pass may also be used to establish the speed with which a project can be completed within the specified timeframe. On the other hand, Backward Pass comes in handy as a second method of computation to establish how one can initiate a project lately without hampering efficient completion of the project (Wiest & Levy, 2005). Some of the Forward Pass calculations are for instance: Early Finish (EF), Late Start (LS), and Late Finish (LF).

Thus the main objective accomplished in Forward Pass is to determine the network’s duration. As earlier mentioned Forward Pass ascertains the early start ‘and finish of each of the activity’ and thus outlines the critical path within the network. Forward pass is calculated by as follows: Early Start = Early Finish of the preceding activity, Early Finish = Early Start + duration of activity. On the other hand, Backward Pass facilitates finish times which may occur without altering the current network relationships.

In Backward Pass, the relevant values are obtained by tracking back calculations in the previous activity within the network (Venkateswarulu & Raman, 1993). Consequently, one is required to work backward by subtracting consecutive time duration ‘from the early finish of activity being calculated’. It is calculated as: Last Start (LS) = Last Finish (LF) – duration of activity. Upon calculating Forward Pass and Backward Pass, one can comfortably calculate the Float/Slack time of the project.

Float time is calculated by finding the difference between the earliest possible start of an activity (Forward Pass) and the earliest possible start of an activity computed from the Backward Pass. If the Float/Slack time is positive, there is probability of delaying activity without delaying the project. Secondly, if the Float time is zero, a delay in activity leads to delaying the whole project as well. Finally, a negative Float indicates the project is far much behind the schedule and besides the negative time represents the magnitude of delay the project.

In other words, Forward and Backward Passes are vital in establishing Slack/Float time so as to specify available spare time in a non-critical activity (Wiest & Levy, 2005) . References Render, B. , & Stair, R. M.. Jr,. (1982). Quantitative analysis for management. London: Allyn and Becon Inc. Venkateswarulu, K. , & Raman, K. V. (1993). Project management techniques for R&D in agriculture. New Delhi: Sterling Publishers Pvt. Ltd. Wiest, J. D. , & Levy, F. K. (2005). A management guide to pert/cpm. New Delhi: Prentice Hall of India.

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