__The Forward Pass__

__The Forward Pass__

We can now calculate how long the project will take. Start by calculating the shortest time or **‘earliest finish’**. Thus, if we start at time ‘0’ the earliest day that ** Designing** can be finished is day 10. Therefore, the process of obtaining

**cannot start until day 10: the earliest we can start obtaining approval is day 10, so the earliest finish for obtaining approval is 10 + 14 = day 24.**

*Approval*The earliest start time is written in the top left-hand corner of the task box, and the earliest finish time is written in the top right-hand corner of the task box.

For the ** Approval** task, we thus say the

**Earliest Start Time (EST)**is 10 and the

**Earliest Finish Time (EFT)**is 24.

The earliest time both ** Approvals** and

**can start is day 10. So, the earliest finish time for**

*Prepare site***will be 24 and for**

*Approvals***day 17. However,**

*Prepare site***cannot start on day 17 because**

*Lay foundation***has not been completed.**

*Purchase materials*Note that the task ** Prepare site** has some

**float**or

**slack**– it cannot start before day 10 and must finish before day 31 (start of

**), but as it only takes 7 days, there is a slack of 31 – 10 – 7 = 14 days.**

*Lay foundation***When calculating the earliest times, one must consider all the paths or arrows coming into the task box and select the largest or longest time**. Completing all the timings, or “Forward Pass” will result in a network picture as shown in Figure 3. The calculations show that the entire project will take 99 days- the ‘earliest finish time’ is 99 days.

__Slack__

You may recall that the task ** Prepare site** had some slack available. The other tasks (i.e., those with no slack) are critical in that any delay in their completion will cause the entire project to be late. Thus, it is very important to discover the critical tasks and identify the critical path through the network.

__Critical Path__

Next, we need to find the Critical Path- **the shortest time path through the network**. In such a simple network it is easy to calculate the amount of slack available for each task. However, in complicated networks it is not easy to ‘see’ which tasks have slack and which zero slack.