All language subtitles for 2. Kinds Of Links, And Leads And Lags

First, some definitions.
2

There are four kinds of precedence links you can use,
3

but only the finish to start link is practical
4

in the vast majority of situations.
5

So first, finish to start.
6

The predecessor must finish
7

and then the successor can start.
8

It's shown with an arrow from the end of the predecessor
9

to the start of the successor.
10

These will suffice for almost all uses in most projects.
11

However, for completeness, let's look at the others.
12

In case you ever find an unusual situation
13

where you want to use one of them.
14

There's finish to finish
15

where the successor must finish
16

at the same time as the predecessor.
17

The arrow goes from the end of the predecessor
18

to the end of the successor.
19

Then there's start to start
20

where the successor must start
21

at the same time as the predecessor.
22

The arrow goes from the beginning of the predecessor
23

to the beginning of the successor.
24

And then finally,
25

there's start to finish
26

where the successor must finish when the predecessor starts.
27

The arrow goes from the beginning of the predecessor
28

to the end of the successor.
29

If these last three seem a bit mind bending,
30

that's normal.
31

You can use them and enter them in the Gantt Chart tool,
32

but in practice you usually structure your project
33

to use only finish to start,
34

which is by far preferable since it's so human intuitive.
35

And that's the main purpose of the precedence diagram,
36

to communicate with people.
37

We'll only use the finish to start links
38

in the rest of the course.
39

You can also use finish to start links
40

to show leads and lags,
41

usually when entering them into the Gantt chart tool.
42

See the schedule section.
43

For leads, you can show overlapping deliverables
44

where the successor starts
45

a bit before the predecessor finishes.
46

Typically used only to show fast tracking,
47

as we'll cover in the Monitoring and Control section.
48

They're specified in the Gantt chart tool
49

with notation like FS minus 5d
50

for Finish to Start minus five days.
51

Here's an example where the successor starts five days
52

before the predecessor is finished.
53

Then you've got lags to show a delay between deliverables,
54

typically used for empty waiting time.
55

They're specified in the Gantt chart tool
56

with notation like FS plus 10d
57

for Finish to Start plus 10 days.
58

Here's an example where the successor starts
59

10 days after the predecessor finishes.
60

However, as described earlier in the WBS section,
61

if the delay between two deliverables
62

is caused by an external event,
63

it is usually better to actually show the delay
64

as a separate deliverable to highlight its visibility.