## Total Float

Total float, in contrast to other types of float, does have a role to play. By definition, it is the time between the anticipated start (or finish) of an activity and the latest permissible start (or finish).

The float can be either positive or negative. A positive float means that the operation or activity will be completed earlier than necessary, and a negative float indicates that the activity will be late. A prediction of the status of any particular activity is, therefore, a very useful and important piece of information for a manager. However, this information is of little use if not transmitted to management as soon as it becomes available, and every day of delay reduces the manager's ability to rectify the slippage or replan the mode of operation.

The reason for calling this type of float 'total float' is because it is the total of all the 'free floats' in a string of activities when working back from where this string meets the critical path to the activity in question.

For example, in Figure 21.10, the activities in the lowest string J to P, have the following free floats: J = 0, K = 10 - 9 = 1, L = 0, M = 15 - 14 = 1, N = 21 - 19 = 2, P = 0. Total float for K is therefore 2 +1 +1 +1 = 4. This is the same as the 4 shown in the lower middle space of the node.

It is very easy to calculate the total floats and free floats in a precedence or Lester diagram. For any activity, the total float is the difference between the latest finish and earliest finish (or latest start and earliest start). The free float is the difference between the earliest finish of the activity in question and the earliest start of the following activity. Figure 24.9 makes this clear.