Monitoring progress

Histograms and 'S' curves are particularly useful for progress monitoring purposes and for the identification of trends. Figure 17 is a very simple 'S' curve that tracks the actual quantity of concrete poured against the anticipated planned quantity.

It shows that the concrete poured up until around week 7 was slightly ahead of the quantity planned. From this point on the general trend has been for actual pours to increasingly fall behind those planned.

This cannot be taken as a definitive measure of progress however as the example would serve as an 'early warning' indicating that as at week 8/9 concreting operations were starting to fall behind the planned intent.

Figure 17: Simple 'S' curve

A more formalised approach to the use of 'S' curves for the monitoring of overall progress was produced in the early 1980s by the Property Services Agency (the 'PSA') which they called 'Planned Progress Monitoring'.

The method relies on the production of a traditional bar chart with the resulting 'S' often superimposed on top. Figure 18 below shows a typical layout for the Planned Progress Monitoring technique.

For each week of the project the number of activity bars occurring in that week are counted and recorded, usually on the bottom of the bar chart in this example as 'activity weeks'. For this reason, planners often refer to it as 'counting the squares'. The cumulative total of these 'activity weeks' can then be calculated and plotted as a simple line graph or 'S' curve depicting the anticipated planned progress.

Figure 18: Typical planned progress monitoring layout

As the works proceed the progress achieved each week is recorded by shading the relevant activity bar lines. At each progress update the number of 'activity weeks' actually achieved can be counted and the cumulative total plotted to produce a line showing progress achieved. The difference between the planned progress 'S' curve and the progress achieved curve can be compared and any shortfall in overall progress noted.

Figure 19: Planned and actual progress

Figure 19 shows the typical Planned Progress Monitoring layout with the progress recorded. It shows that the bar chart has been shaded to indicate the progress achieved with the activity weeks achieved being recorded for each week. The cumulative total of these activity weeks has then been calculated and an 'actual' 'S' curve plotted (with a dotted line in the above).

It indicates that the progress achieved is less than that planned and that at the time that the progress was recorded only 43 activity weeks had been achieved compared with a planned total of 63.

This methodology overcomes one of the disadvantages of the simple bar chart, in as much as it gives an indication of the overall project progress. It must be stressed that the planned progress technique simply indicates the cumulative total of all of the progress recorded which implies that all general progress is valuable progress; it takes no account of the required progress of the critical activities.

Any sole reliance on the results of the planned progress monitoring technique is likely to prove misleading. The results can give a good indication of a problem area, particularly if the shortfall in progress continues to deteriorate at every progress update. Therefore, the methodology should be considered as a useful indicator of ongoing trends rather than as a definitive measure of progress and project status.