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Unformatted text preview: erformance Ratio curve that should concern the project manager. If this curve stays near the value of 1, then chances are the cost performance on the project will continue to be good. Of course, there can be trends in the period CPR curve that indicate a deteriorating situation. For instance, if the period cost performance ratio stays low for two or more periods in a row, then there may be some cause for concern. Another trend in the period CPR curve for which the project manager needs to watch is if the period CPR stays high for Page 149 several periods in a row. This indicates that either exceptional cost performance is being achieved or that, purposely or unknowingly, the expenditures are being consistently understated or the progress is consistently being overstated. The latter of these two possibilities is the more common. The project manager does not want to get lulled into the conclusion that everything is going well just because the reports and charts indicate high performance scores. The behavior of the two CPR curves in Figure 6-8 is very typical of real projects. If the period cost performance curve does not oscillate or if the total cost performance curve does not approach some value asymptotically, then the project manager should find out why. Figure 6-9 is the new Schedule Performance Ratio (SPR) trend chart. Notice that for the last month (February '01) the Period Schedule Performance Ratio is zero, and yet the Total (cumulative) Schedule Performance Ratio increases during the month. How can this be? The answer is that the Period Schedule Performance Ratio for February '01 is really not zero, but rather nonmeasurable. Modern Project uses zeros in both the Figure 6-9. New Schedule Performance Trend Chart from new transactions. Page 150 Cost Performance Trend Chart and the Schedule Performance Trend Chart to indicate either a value of zero or that the ratio cannot be calculated. The reason the Period Schedule Performance Ratio cannot be calculated for February '01 is that 200 labor-hours were earned during that month, but the control budget for February '01 does not increase over the January '01 control budget as shown by the current baseline graph (Figure 6-2). Consequently, the calculation of the Period Schedule Performance Ratio for February '01 would involve dividing 200 by zero, which is not a meaningful value. So it is not possible to calculate the Period Schedule Performance Ratio for the period February '01. Modern Project detects this and inserts a zero instead for the Period Schedule Performance Ratio for February '01. The behavior of the Schedule Performance Ratio curves is likely to be similar to the Cost Performance Ratio curves. Often, however, it is the case that the total cost and the total schedule performance ratios do not asymptotically approach the same values. This is simply an indication that one of the two ratios is not as good as the other. It is common to see projects that have good cost performance and poor schedule per...
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- Spring '10