Figure 9-22. - PDM network with total and free float calculations.

The free and total float times are the amount of scheduled leeway allowed for a network activity, and are referred to as float or slack. For each activity, it is possible to calculate two float values from the results of the forward and backward passes.

TOTAL FLOAT. - The accumulative time span in which the completion of all activities may occur and not delay the termination date of the project is the total float. If the amount of total float is exceeded for any activity, the project end date extends to equal the exceeded amount of the total float. Calculating the total float consists of subtracting the earliest finish (EF) date from the latest finish (LF) date, that is:

FREE FLOAT. - The time span in which the completion of an activity may occur and not delay the finish of the projector the start of a successor activity is the free float. If this value is exceeded, it may not affect the project end date but will affect the start of succeeding, dependent activities.

Figure 9-23. - Independent activity.