Calculating progress on parent tasks according to cost complete
This topic describes in detail how the progress marking on
When progress on parent tasks is calculated according to cost complete, the cost of cost allocations and
Note that while the contents of hammock tasks are excluded from the calculations, any allocations that are made directly onto a hammock task affect the progress date of the hammock task itself - although this is not rolled up any further to parent tasks at a higher level.
Powerproject calculates progress on parent tasks according to cost complete in a similar way to that in which it calculates progress according to duration complete. It creates a 'profile' of values against time, but this time to represent the distribution of cost.
Consider the following scenario, in which a summary contains three tasks. Two of the contained tasks and the summary itself have one or more cost allocations. Note that each working day is 8 hours long in this example:
Powerproject creates a 'profile' of cost against time, to represent the distribution of cost. Here is a description of the allocations in order, from the top down, with a description of how much cost each one contributes towards the profile:
- The first allocation (cost £300; duration 16h) contributes £0.006 per second in the profile (£300 / 16h = £18.75 per hour, or £0.006 per second).
- The second allocation (cost £75; duration 8h) contributes £0.003 per second in the profile (£75 / 8h = £9.38 per hour, or £0.003 per second).
- The third allocation (cost £350; duration 8h) contributes £0.012 per second in the profile (£350 / 8h = £43.75 per hour, or £0.012 per second).
- The fourth allocation (cost £187.50; duration 20h) contributes £0.003 per second in the profile (£187.50 / 20h = £9.38 per hour, or £0.003 per second).
The resulting profile is illustrated below (note that
The total amount of completed cost contributed by the allocations is as follows:
- The first allocation (cost £300; 50% complete) contributes £150 of completed cost.
- The second allocation (cost £75; 0% complete) contributes no units.
- The third allocation (cost £350; 0% complete) contributes no units.
- The fourth allocation (cost £187.50; 40% complete) contributes £75 of completed cost.
The total amount of completed cost in this example is therefore £225. The progress date for the top-level summary task is calculated by finding the date at which the cumulative area underneath the graph equals £225.
The areas of the sections in the above profile (from left to right) are as follows:
- Section 1: £0.006 x 14,400 = £86.40 (14,400 being the number of seconds in a half day in this example).
- Section 2: £0.009 x 14,400 = £129.60; sections 3 and 4 are identical.
- Section 5: £0.018 x 14,400 = £259.20; section 6 is identical.
As the cumulative value to the end of the second section is £216.00 and the cumulative value to the end of the third section is £345.60, the progress date (equivalent to £225) lies somewhere within the third section. A simple ratio shows that the date lies towards the start of the section - early on Tuesday morning.
Mixed calendars and durations measured in elapsed time
The procedure for calculating the progress of parent tasks according to cost complete when tasks use different calendars is identical to that described above.
When a task's duration is marked in elapsed time, it is assumed that work takes place continuously on the task for 24 hours per day and the task's calendar is ignored.
Nested hammock tasks
As mentioned previously, allocations made to nested hammock tasks and their contents do not contribute towards the progress of any summary or expanded tasks in which they are contained. This is because it is assumed that the contained allocations will be taken account of elsewhere in the project.
For the purpose of calculating progress on parent tasks, milestone allocations are given a nominal duration of one second.
Calculating progress on parent tasks according to the Cost - Approximate method
If you are working with a very large project, you may find that calculating the progress on parent tasks takes a considerable time. You can reduce the amount of time that it takes by selecting the Cost - Approximate method of progress calculation in the Progress method field that appears both on the Progress tab of the Options dialog and on the Properties tab of the Properties dialog.
This method works in a similar manner to that outlined above, but the effect of calendars is ignored in large projects, which simplifies the calculations. Normally, the contribution of a single allocation to the cost distribution is a value of 1.0 during working time and 0 during non-working time; if the Cost - Approximate method is used, a single value is used throughout an allocation's duration.
The value that is used depends on the ratio of working time to non-working time, so that the area under the profile for an allocation is the same as it would be if the profile dropped down to 0 during non-working time. So if an allocation started at 09:00 on Monday morning and finished at 17:30 the following day (assuming 7.5 hours of working time per day), there would be 15 hours of working time in the allocation's duration and 16.5 hours of non working time. Therefore a constant value of 15 / (15 + 16.5) = 0.476 would be used throughout the allocation's duration.