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For many of us, creating the network diagram can be very complicated and

Â daunting, especially the first few times through it.

Â There are a few of you who can look at a list of activities

Â along with their estimates.

Â And you can see the schedule right in your head.

Â You get the picture right away.

Â But most of us need to practice creating a network diagram multiple times,

Â multiple times.

Â More than one, more than two.

Â More than once, more than twice.

Â With this thought in mind let's walk through it again and

Â be sure to pause this video as many times as you want.

Â And watch parts of it over as many times as you want.

Â Because it's for you.

Â So this is about you and your learning.

Â Please don't cheat yourself.

Â What you have is you've got, see this area here?

Â I'm gonna highlight it here for a minute.

Â This is work.

Â Now, this is a project for building a stage.

Â Allegedly cuz it's simplified for us, so

Â I'm sure that building a stage is more than this.

Â 1:19

And then we have a duration.

Â And I'm gonna say days, even if that's crazy.

Â Maybe it's a really big stage.

Â But I'm just gonna use days cuz it's simple to talk that way for me.

Â And then what we have over here is predecessor, what comes before.

Â What comes before.

Â And you remember that if an activity has no predecessor, which is true of

Â items one and two then they are the first pieces of work that can occur.

Â So keep that thought in mind.

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Over here, let me highlight this, we have a legend, and that

Â legend is showing us these rectangles that we're using to map out different fields,

Â because we are going to be like computer project scheduling software and

Â we're gonna do some calculations.

Â And the calculations that you and

Â I are doing are what your scheduling software does actually do for us.

Â So we have the rectangles divided up with little legends,

Â see in this top corner here, top left-hand corner, it's ES.

Â That means early start, what is the soonest that this piece of work can begin?

Â Here we have just an identifier, which is the activity number.

Â 2:55

Duration, which just comes from the table over here.

Â How long is it gonna take.

Â Just like the activity number came from the table over here.

Â And LF light, again, LF like Frank or finish which is what it is, late finish.

Â What is the latest this can finish?

Â And we mean, without delaying the project,

Â or without delaying the work that happens after it as well.

Â Now, what we do to find out the path of the project

Â is we do what's called a forward pass, and we do what's called a backward pass.

Â And the forward pass involves you and

Â I going through this network diagram down here from left to right.

Â And that is the forward pass.

Â And we go through each activity and were gonna calculate, on a forward pass,

Â what is the early start and what is the early finish for each piece of work.

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When we do a backward pass, then we are going from right to left, so

Â we're going from the end to the beginning, and

Â we are calculating the late start and the late finish.

Â So we need the forward pass and then the backward pass.

Â When we have finished both, then we can calculate the float.

Â So where did this diagram come from?

Â That, just, this, Here, comes from this up here.

Â So remember when I said if an activity has no predecessor, it means that could be

Â the first work, so activity 1 and 2 neither have predecessors, so

Â when we draw our network diagram, we know that 1 and 2 can both happen

Â at the start of the project, and that also means since they don't have a predecessor,

Â they can both happen in parallel, so that's how we draw them.

Â 4:46

Now activity 3 has predecessor of 1 and 2.

Â So activity 3 cannot start until 1 and 2 finish.

Â And by the way, when we do draw these, we do assume a finish start relationship.

Â So 1 must finish before 3 can start.

Â 2 must finish before 3 can start.

Â 5:06

Now, activities four, five, and six, look at them.

Â 3 is a predecessor to all of them, and since they have no other predecessor,

Â we know that, all other things being equal, those three activities,

Â installing the lights, installing the sound, and installing the seats

Â can all happen at the same time, they just have to wait for 3 to finish.

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We have parts of our legend for each one filled in, cuz we have the activity and

Â the duration filled in on each item.

Â And by the way, I always recommend that.

Â Do the easy stuff first.

Â So go in, once you have the work mapped out, once you have this structure drawn.

Â Go into each one and fill in the activity and the duration for each one,

Â because it helps you, because you're gonna use it in the calculation, now,

Â let's begin our forward pass.

Â 7:07

So let's fill that in and then we'll come back and talk about that for a minute.

Â So early finish goes here.

Â It's the early start which is 1, plus the duration which is 20.

Â Which is now that makes that 21 minus 1, which makes it 20.

Â That goes there, over here 1 plus

Â 10 minus 1, gives me 10.

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Think of it this way, we're gonna start the work at the beginning of the day.

Â And when we finish, we finish at the end of the last day.

Â Okay.

Â Now I'm gonna use an easy example now,

Â because I'm gonna run out of fingers otherwise.

Â And I will often do this on my fingers, that if I'm standing in front of a group

Â of people, I will actually count it out on my fingers.

Â But think about this, let's say we had a piece of work and it was five days.

Â We started on the first day.

Â 8:26

Now think about it.

Â If it's five days, and

Â I really finish it at the end of the last day, Here's how it works.

Â I work one day, I work two days,

Â I work the third day, I work the fourth day, and I work the fifth day.

Â At the end of the fifth day, I'm done.

Â 9:28

We use the highest early finish, of the predecessors, the highest early finish.

Â That means we're gonna use the 20, because 20 is greater than 10.

Â See, that's not hard.

Â That's not difficult.

Â We use the 20.

Â Now, what's the formula?

Â The formula is that predecessor plus 1.

Â So I take 20,and I add in 1.

Â So I start activity three on day 21, and

Â that makes sense because activity one ended at the end of day 20.

Â So we come back in the next morning, and we start off activity three.

Â Now why would I take the predecessor, the highest early finish?

Â Why would I take the highest number?

Â You know this, of course.

Â Because, if I have to wait for

Â two things to finish, both these items have to finish before I can start three,

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Now, to do the early finish.

Â It's our same old thing again, we take the early start.

Â Here's our formula again.

Â Plus the duration minus 1.

Â So 41+5 is 46-1 is 45.

Â 41+10 is 51-1 Is 50.

Â 41+7 is 48-1 is 47, and there we go.

Â Now we're at the very last activity.

Â And again, I have to make a choice, because there's more than one predecessor.

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So again, I used the highest early finish, because if it must wait for

Â everything, all three of those activities, to finish before it can start.

Â It cannot start until the last one begins.

Â So that means I used the early finish of 50, because that's the highest one.

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It's the same number as the early finish.

Â I said late start, didn't I?

Â Pardon me, late finish.

Â The late finish of the last activity is easy,

Â because the late finish is the same as the early finish.

Â We either finish or we don't.

Â There's not two finish dates.

Â So that's nice.

Â That's 52.

Â Now how do I get my late start, which should go right here?

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Now I have to figure out the late starts for all of them, and

Â it's the same thing again.

Â Which is the late start is the late finish minus the duration plus 1.

Â So 50- 5 + 1.

Â So 50- 5 is 45 + 1 is 46.

Â Now, here we go.

Â 50- 10 + 1.

Â 50- 10 is 40 + 1 is 41.

Â And now I have 50- 7, 43.

Â Getting dingy here, and that's 43- 1 is 42.

Â So let's step back and make sure that's correct.

Â 15:32

Now, our late start, again,

Â is equal to late finish minus duration plus 1.

Â So that's how we got our 50- 5 + 1 is 46.

Â My 50- 10 + 1 is 41.

Â And my 50- 7 + 1 I have a hard time doing it sometimes too,

Â you guys, I apologize for that.

Â Let's look at this last one, I think this last one is wrong.

Â 50 minus 7 is 43, plus 1 is 44, that's where were off.

Â Yep, there we go.

Â Okay, thank you for being patient with me.

Â Now, we have an activity that has more than one

Â successor, and that's this guy right here.

Â So activity three has three successors,

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and that means we have to make a choice in terms of what

Â late start to use to work backwards because there's three choices.

Â I could use 46, 41, or 44.

Â So what do you think I should use?

Â When we are doing the backward pass,

Â we use the lowest number.

Â We use the lowest number.

Â So let's do that and form the calculation.

Â What's the lowest late start over here?

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So now, I get my late finish here is equal to 41 minus 1.

Â Whew, I can do that one.

Â It's 40. And now to get my late finish, again,

Â I am, or my late start, I apologize that I keep messing this up.

Â To get my late start, I now take 40,

Â which is the late finish,

Â minus the duration, which is 20, plus 1.

Â So that gives me 21.

Â Whew, okay, now back here I have only one late start

Â to move forward to make it into the late finish, right?

Â So, this becomes 20, and this becomes 20.

Â Because remember the formula for late finish is to take the late start and

Â subtract one.

Â And now, thank goodness we're on the very last two where we're working backwards,

Â and we're figuring out our late starts.

Â And so we take that late finish, subtract out the duration, and add in one.

Â So 20 minus 20 is 0, plus 1 is 1.

Â And 20 minus 10 is 10, plus 1.

Â Now you see the picture that's being painted here?

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we could have a different start and a different finish.

Â Why wouldn't we just start and finish all at the same time?

Â But what this picture is showing us, what we've just figured out, is that there

Â are some times where there are pieces of work activities that can be delayed, and

Â it won't delay the end of the project.

Â So if we're calling these days, and we're saying right now this is day 52,

Â we don't want anything to happen to make it go to day 53.

Â And so what we have is work that has to happen exactly

Â on certain days in order to make it to day 52.

Â That's the critical path.

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When we look at some of the pieces of work here,

Â we can see that there's a difference between some of their late starts and

Â early starts, and late finishes and early finishes.

Â And when that happens, we have a value for float.

Â And so what we wanna do next is go through and calculate float.

Â And float is gonna go in here, this section.

Â And float, you can use two different calculations,

Â cuz if I've done this correctly, and

Â I hopefully corrected my errors that I had earlier, I'm gonna get the same number.

Â So float is either late start minus early start, or late finish minus early finish.

Â Now, let's step back. Your critical path is the tasks or

Â activities that have zero float.

Â Those are the items that have to absolutely finish per plan,

Â or we're gonna be late.

Â And now you can see here,

Â if you've been wondering why some of this was highlighted,

Â that's because I had left some of the highlighting in.

Â The items that have float are actually shaded in yellow on here.

Â And so if you just now go back to the beginning, and

Â we look at these first two activities, activity one and two.

Â They both could start at the beginning, but one took 20 days and one took 10 days.

Â Right away, you probably knew that that meant that the second activity

Â which took ten days which was buying supplies probably could wait a few days.

Â Because what was really driving the schedule,

Â was the 20 days we needed just to take to hire the workers.

Â Then, since activity three is next and it is the only next thing,

Â it makes sense that that's the critical path.

Â Then when we get to installing the lights, the sound, and

Â the seats, what drives the completion of the project is whichever one of those

Â items is going to take the longest amount of time.

Â Which one is going to take the longest?

Â Installing the sound.

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And installing the seats has three days of float.

Â Now the last activity has no float, and that makes sense as well.

Â If it's the very last thing that happens and

Â it's the only item that happens at the end, it can't have float.

Â It needs to finish in order for us to finish up on day 52.

Â So that's our forward pass, our backward pass, our floats,

Â our critical path, and that's our day one approach using.

Â Whew, all right, great job.

Â Thank you for sticking with it.

Â And remember, for

Â most of this, the network diagram takes practice, practice, practice.

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It's worth it though because when you understand the critical path and

Â where you have float, and what is driving your project schedule,

Â you have mastered one of our critical project management concepts.

Â So thanks for hanging in there.

Â