A network is always scheduled forwards and backwards. The scheduling type specifies whether forward scheduling or backward scheduling is carried out first.
Forward scheduling calculates the earliest start and finish dates for the activities. All activities that do not have predecessors are start activities. The scheduling start date is the start date in the network header or the start date determined from backward scheduling.
Backward scheduling calculates the latest start and finish dates for all the activities. Last or finishing activities are network activities that do not have successors. The scheduling start date is the finish date in the network header or the finish date determined from forward scheduling.
In the preceding figure, the start dates are set to the beginning of the day (00:00) and the finish dates to the end of the day (24:00). If work centers are entered for the activities, the start and finish dates are within the operating time of the work centers affected.
Total Float, Free Float
| ES= Earliest Start | EF= Earliest Finish |
| LS= Latest Start | LF= Latest Finish |
| TF= Total Float | FF= Free Float |
Floats supply information on the time reserves available for individual activities. For example in capacity leveling, you can use the floats calculated in scheduling to shift activities between the earliest and latest dates or to extend their duration.
Example of Floats
The preceding figure describes how total floats and free floats are calculated.
The total float of activity 40 can be calculated from the difference between the earliest and latest start of an activity:
Day 6 (0:00) - Day 5 (0:00) = 1 day.
The free float of activity 40 can be calculated from the difference between the earliest start of the successor (activity 50) and the earliest finish of the activity.
Day 9 (0:00) - Day 7 (0:00) = 2 days.
