Calculating the
Forward Path
Figure 7-5 shows
a simple network with the forward path calculation.
We must adopt a notation convention. The tasks will be shown in
rectangular boxes; the earliest start date will be on the upper left corner, and
the earliest finish will be on the upper right corner. The corresponding lower
corners will be used for latest start and finish dates, respectively. Duration
will be shown in the rectangle.
In the forward path calculation, notice the use of the earliest
start dates. The basic rule is simple:
Earliest start date + Duration = Earliest finish
date
Now we have to be cognizant of the various precedence
relationships such as finish-to-start and finish-to-finish, etc. All but
finish-to-start greatly complicate the mathematics and are best left to
scheduling software. Therefore, our example networks will all use
finish-to-start relationships. There is no loss in generality since almost every
network that has other than only finish-to-start relationships can be redrawn,
employing more granularity, and become an all finish-to-start network.
Working in the forward path with finish-to-start relationships,
the rule invoked is:
Earliest start of successor task = Latest of the early finish
dates of all predecessors
The final milestone from the forward path analysis is an
"earliest" finish milestone. Again, unless explicitly shown, any final
management reserve task of unallocated reserve task is not shown for simplicity.
If it were shown, it would move out, or shift right, the final milestone to
align with the program milestones from the business side of the balance
sheet.