Late Finish - Duration = Late StartLate Start - Lag (if any) = Late Finish (precedingactivity)TOTAL FLOAT.— Total float is the number ofdays an activity can be delayed without delaying theproject completion date. Looking at activity 0311 infigure 2-31, you see that it could finish as early as day10 or as late as day 12. The 2 days of leeway betweenday 10 and day 12 inactivity 0311 are called total float.To calculate the total float, you subtract the early finishdate from the late finish date or the early start datefrom the late start date. The numbers will be the same.If not, you made a math error.Total Float = Late Start - Early Start (or LateFinish - Early Finish)FREE FLOAT.— Free float is the number of daysan activity can be delayed without taking float awayfrom the next activity. Another way of saying the samething is that free float is the number of days an activitycan be delayed without delaying the early start date ofthe next activity. To calculate the free float for anactivity, you subtract any lagtime and the early finishfor the activity from the early start for the next activity.To calculate the free float for activity 0311 in figure2-31, you would take the early start for activity 0312,subtract any lagtime between 1020 and 1050 (zero inthis case), and subtract the early finish for activity0311 (11 - O - 10 = 1). Free float for activity 0311 is1 day. You can see that delaying activity 0311 by 1day will not delay activity 0312 from its early startdate. Delaying activity 0311 by 2 days will delay thestart of activity 0312 until day 12 and reduce the floatfor activity 0312 by 1 day (to zero, in this case). Thedelay of activity 0311 by more than 2 days will delaythe project completion date because 0311 has only 2days of total float.Free Float = Early Start (next activity)- Lagtime (if any) - Early FinishCRITICAL PATH.— Looking at activity 0311 infigure 2-31, you could start that activity as early as day3 or as late as day 5. Now subtract 3 from 5 and enter2 days as the total float. Where the early start and latestart are the same, there is no float. “No float” meansyou have to start that activity on its early start date. Itcannot be delayed without delaying the projectcompletion date. Activitieswithnofloataresaidtobecritical.The first and last activities will always becritical, and there will be a critical path of activitiesbetween them. The critical path in figure 2-31, is0151-0211-0322-0331. The critical path allowsmanagement to focus attention on those activities thatcannot slip.Advantages of DiagramsPrecedence networks are easy to draw because allthe activities can be placed on small cards, laid out ona flat surface, and easily manipulated until a logicalsequence is achieved. It is also easy to show theinterrelationships and forward progress of theactivities. Just draw connector lines. Figure 2-32Figure 2-31.—Logic network.2-46

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