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Floats in the AoA network
Project management(lecture)
Activity and event times
• Activity times:– EST– LST– EFT– LFT
• Event times:– EET– LET
Float• Time available for an activity or path in
addition to its duration.• It can be positive or negative• It is a property of activities (and available only
at given activities)• In case of more succeeding activities, the
minimum have to be taken.• Types of float:– Total float– Free float
Total float• The total float possessed by an activity. • Calculation for activity j:
Total floatj = LFTj – EFTj
• Identify the activity possessing float below, and calculate the total float.
10
?
2?
?
a
12
4?
35
c
10
3?
?
b
15
d
8
Total float• The total float possessed by an activity. • Calculation for activity j:
Total floatj = LFTj – EFTj = LFTj – (ESTj + Dj)
• Identify the activities possessing float below, and calculate the total float for each.
10
0
25
11
a
5
423
23
c
12
315
15
b
15
d
8
Total float = 23 – (5+12) = 6Total float =
= 11 – (0+5) = 6
Calculating free float• The float possessed by an activity which, if used,
will not change the float in leater activities.• Free floatj = ESTj+1 – EFTj = EEThead – EETtail - D
10
0
25
11
a
5
423
23
c
12
315
15
b
15
d
8
Free float = 23 – 5 – 12 = 6Free float =
= 5 – 0 – 5 = 0
Negative float• If the target time (deadline) for the project (or for a part
of the project) is grater than TPT, than the float will appear on the critical path or even on some other paths.
• Negative float = the time by which activities on the path or paths concerned must be reduced if the TPT is to be met.
• Negative float is a type of the Total Float.
10
?2
?
?a
10 3?
?c
10
30
Negative float• If the tartget time (deadline) for the project (or for a
part of the project) is grater than TPT, than the float will appear on the critical path or even on some other paths.
• Nagative float = the time by which activities on the path or paths concerned must be reduced if the TPT is to be met.
• Negative float is a type of the Total Float.
10
-52
10
5a
10 320
15c
10
15
Total float: -5Total float: -5
Slack• Refers to events and not to activities.• Slack = LET - EET
Slack: 0
10
0
25
11
a
5
423
23
c
12
315
15
b
15
d
8
Total float = 23 – (5+12) = 6Total float =
= 11 – (0+5) = 6
Slack: 0
Slack: 0
Slack: 6
Readings
• Lockyer – Gordon (2005) Chapter 13
Thanks for the attention!
10
0
27
11
a
7
423
23
c
10
315
15
b
15
d
8
