Try it the old way: say you try 3 tasks A, B and C. You then create Task D whose dependence on Task A is SS and whose dependence on Task C is FF. It will stubbornly have its own Duration regardless of the duration of Tasks A, B and C.

We need a solution so that Task D will have the same Duration as Tasks A, B and C no matter what happens to the Start of Task A and the Finish of Task C.

This is needed in situations such as:

• Assigning a supervisor to an Effort Driven Task such as pouring concrete. You need to have a separate Task in order not to confuse Microsoft Project with the changes in the units of the concrete pouring Resources. The supervision effort must be expressed as a Task that expands or contracts depending on how you manage the pouring concrete task, ie, their Duration must be the same.
• Project Management Tasks that span the whole project
• Tasks wherein you assign overheads (that also span the whole project)
• Tasks which span other Tasks where the resource assignment is wildly different

what is commonly known as a Hammock task will do the trick. It will have the same Duration as the whole project or as a specific task it is spanning. But there is no automatic or direct way of creating a Hammock Task.

Please download the PDF file that has a fully detailed procedure to create a Hammock Task (Click here).

Also, the next post shows a very useful and practical example using the Hammock Task (Click here).

In many situations, you want to charge a resource across working days but you want to charge his/her expenses across calendar days.

Example: We have an engineer working for 8 days, starting on a Monday. The engineer will be staying in a hotel where the cost per night is $200.

During this period there is one weekend. However, if the engineer starts work on Thursday, we will have 2 weekends. Secondly, the duration of his/her work might change, so the number of weekends cannot be known in advance.

• If we use Material or Cost Resources for Hotel Nights, these will be charged for 8 days only. Remember both Material and Cost Resources do not have calendars, so we cannot force weekends upon them.
• If a parallel Task is created to which we assign Material or Cost Resources, we can use elapsed duration. Two problems with this approach. First: we have to specify the duration of the parallel task which defeats the purpose of our work. Second: Microsoft Project will charge 24 hours per day and for 8 consecutive days.

There is no direct way to force Microsoft Project to charge Hotel Nights across the calendar period.

Please download the PDF file that shows the solution to the above case (Click here).

Also, the previous post shows a detailed procedure on how to create a Hammock Task (Click here).

A confusing facility in Microsoft Project is the way Duration, Units of Resources and Work Loads per Task are interact with one another.

The Work Formula is clear: Work = Units x Duration. But there are 2 major options that make Microsoft Project behave in diverse ways, some of them unintuitive. One is a field called the Task Type (Fixed Work, Unit or Duration) and the other is a field that defines whether a Task is Effort Driven or not.

Try as I might, I could not get books, blogs or training material that carried the Work Formula logic to the end.

The time was ripe for Reverse Engineering. We have a black box called Microsoft Project and its Work Formula is programmed to work in ways more mysterious than a Project Manager’s mind. The box has a lot of input and a fewer outputs. Which inputs do we use to which output?

To Reverse Engineer the Work Formula, we will:

1. Analyze the two Task fields (columns): Task Type and Effort Driven
2. Identify all possible combinations of input (scenarios)
3. Try each one to see how Microsoft Project behaves (output)
4. Arrive at a decision logic that allows us to know where to use which setting.

The discussion is length and has been detailed in a PDF white paper.

The white paper is accompanined by Microsoft Project and Excel files which are found in a zipped file

I would be very interested in your comments through this post.

Invariably, someone will ask, “what if we invested more in this or that instrument?” Sure, go ahead and do it, but don’t forget to write down the last output value as it will be overwritten by your new scenario. Now the boss pokes his head in the door and says: can you give me a list of the ROI for each of these different amounts? The insensitive brute has just asked for a sensitivity analysis.

So the real question is: how sensitive is my output to my input? In most cases, you would be happy to see a list of all input values next to the resulting output values. In others, you would want a result that measures the sensitivity. Probably a graph between the input and the output might tell you more about sensitivity. For example, if changing the exchange rate does not result in major changes to the ROI, then the ROI is not sensitive to exchange rate changes. Just think of sensitivity as it applies to your friends and you will know what I mean.

For example, there is an entry on the Data menu called Table. So what else is new? Excel is all tables. Wait, it does not get any better. Select the entry and you get a little dialog box that asks for a row and a column cell. Now what? Now nothing. What are these cells and what do they do? In reality, the Data/Table entry is a very powerful sensitivity feature (although with some limitations). Once you use it, you get addicted to it. It comes under different names that are also not mentioned by Excel as we will see.

Excel has 4 direct facilities to analyze sensitivity. I say direct because there are other indirect facilities which I will introduce below. Here is what is available on the menus:

• What If Analysis (One way table variation)
• What If Analysis (Two way table variation)
• The Scenario Manager
• The Solver

The first two are covered by the Data/Table entry.

The indirect sensitivity analysis that Excel can perform is not based on preset facilities. Rather, you would have to use a combination of formulations using some statistical functions in addition (optionally) to programming the formulation using Excel’s Visual Basic for Applications (VBA). Sensitivity analysis can then be carried out through Monte Carlo Simulation modeling which can do a lot more, as we will see.

The main example is based on a very brief Income Statement. The requirement is to project the budgetary figures for 2007 using actual values from 2006 multiplied by one or more growth factors. Our objective is to see how the Net Profit Margin depends on the Sales Growth used. The formulation shows it for 4%. The What If analysis allows you to vary the Sales Growth from 2% to 12% in 0.5% increments and study the resulting Net Profit Margin.

The last worksheet shows how sensitivity analysis is applied to discounted cash flow whereby the NPV (Net Present Value) is varied against different discounting rates.

Sadly, Excel only allows us these limits: 1) One input variable but one or more output variables and 2) Two input variables but only one output variable. To define more variables, Excel provides us with the Scenario Manager. This is a powerful facility but needs a bit more work to complete. I will show you its intricacies in the next entry.

Download the What If Excel Workbook.