Lesson 1: Your First Model

See Overview of Modeling with ProcessModel video tutorial.

See Learn How to Use the Interface video tutorial.

Operating Parameters and Requirements

In our first lesson we will model a small call center. The objective of this lesson is to find the appropriate staffing level for a given call volume. We will be modifying the model itself, as well as changing some parameters in order to reach the objective.

Help desk staff (Level 1 resource) make $8/hr while support staff (Level 2 resource) make $12/hr.

75% of the calls taken can be resolved over the phone within the first 2 minutes. Once the question is answered, the call exits the system. But the remaining 25% of calls are more difficult and require additional research. The research function takes 20 minutes to complete. Following the research, the call must be returned to the customer. This call back takes 3 minutes.

New calls come into the call center every 5 minutes. Management has determined that the average customers with a difficult issue should not to wait more than 60 minutes to receive a call back.

Open the Model

Download Lesson 1 – Call Center model here.

Start ProcessModel and open the Lesson 1 – Call Center model package by selecting the Open option from the File menu.

This will install the model files from the package but keep the package intact. That way you can change the model as much as needed. Then, if you ever need to go back to the original version of the model, you can just install the package again. Just make sure you use File / Save As to change the name of your model before installing the package again. Otherwise you will overwrite your current model of the same name.

You should now see the model shown below.

Answer the following questions without simulating the model. Supposing 200 calls arrived:

1. How many calls exit without requiring research?
2. How long does each simple call take to complete?
3. How many calls require research?
4. How long does it take to service the difficult calls?

Simulating the Model

To simulate the model, click the Simulation menu and then select the Save & Simulate option.Simulate ProcessModel


The upper left region of the simulation window is called the Scoreboard. It shows some key statistics for entities which have completed the process and left the model. The upper right section of the window shows the simulation clock. 30 hours and 23 minutes into the simulation, the 63 completed difficult calls have taken an average of 681.24 minutes to make it through the process. That may be a surprise since the total activity time for the model is only 25 minutes. One of the benefits of simulation is to demonstrate what will actually happen, rather than what is supposed to happen, or what you think will happen.

You can speed up the simulation or slow it down by dragging the scroll bar at the top of the window to the right or left.

The indicator lights above the resources show their activity. Red means the resource is on break or off shift. Blue means the resource is on shift but waiting for work. Green means the resource is currently working on an entity.

Simulation WindowThe number above and to the left of an activity represents the contents of its input queue. In this case there are 14 calls waiting to be returned because the activity is currently busy. The number below an activity shows the current contents of a multi-capacity location. The Perform Research activity has a capacity of 10, but since there is only 1 Level 2 resource, only 1 entity can be processed at a time at that location.

View the Output Report

Following the simulation you will be asked if you want to see the results. Click No, after returning to ProcessModel click the output report button Output report button.

ReviewProcessModel Output Report

Click the General Report and then goto the Resources section. You’ll notice that the Level 2 resource was busy 96.7% of the time while the Level 1 resource was only busy 40% of the time.

Click the Entity section. There you see that 70 Difficult calls left the model and took an average of 669.69 minutes to do it.

Goto the Activities section. Notice the input queue for the Return Call activity had an Average Contents of 21.76 and an average wait time of 497.37 minutes. That’s over 8 hours in that activity alone before the call was returned. Our manager is not happy!

Solution 1 – Hire More StaffAdding More Staff

Close the output report. Then double click on the Level 2 resource and change the Quantity field to 2.

Save this as a new file by clicking the Save As option on the File menu. Save the file as using the name Lesson 1 – Solution 1. Now simulate your model and find the average cycle time for the Difficult calls.


5. How much improvement was there in the cycle time?
6. How did the resource utilization change?
7. Is that utilization change good or bad?

Solution 2 – Change Entity Handling

While there was a dramatic improvement in cycle time, solution 1 will increase cost. Let’s try another where the Level 2 resource stays with the entity from the time they begin research until after they return the call. Change entity handling

Open the original call center model by clicking File and then Open. Select the Lesson 1 – Call Center model. Change the Get and Free connector from Perform Research to Level 2 to a GET.

Also change the Get and Free connector from Level 2 to Return Call to a Free.

Now, instead of the Level 2 resource being freed immediately after the Perform Research work is complete, the resource will travel with the Difficult call through the Return Call activity until the call is complete and has been returned.

Save this new model as Lesson 1 – Solution 2. Simulate the model.


The average cycle time is now 212.27 minutes which is not as good as in Solution 1. However, there is no increase in cost. The Perform Research input queue has an average contents of 8.28 and an average time of 179.23 minutes.


8. Where is the queue buildup now?
9. What happened to the input queue buildup at Return Call?

Solution 3 – Change Responsibilities

Change responsibilities

Since the Level 1 resource has some free time, let’s see what happens if we have them return calls instead of the Level 2 resource.

Close any models you have open. Open the Lesson 1 – Call Center model. Click the dashed line connecting the Level 2 resource to the Return Call activity. Press the Delete key on your keyboard. Hover your mouse over the Level 1 resource. Then click and drag your mouse to Return Call.

Rename your model to Lesson 1 – Solution 3 by clicking the Save As option on the File menu.


After simulating this new model, you’ll notice the cycle time for Difficult calls has dropped to 105.35 minutes.


10. What was the Average Contents value for the Perform Research input queue?
11. How long did the average Difficult call wait in the input queue of the Perform Research activity?
12. What was the utilization for each resource?

Solution 4 – Alternate Resource

Another alternative is to cross train Level 1 workers so they can help doing research when they aren’t busy taking calls. Remember though, taking calls is their first priority. So if they are doing research and a call comes in, they need to stop doing their research in order to take the call.Alternate resource

Open the Lesson 1 – Call Center model. Hover the mouse over the Level 1 resource. Click and drag your mouse to the line connecting Level 2 to Perform Research.

To place priority on taking calls, click the connector between Level 1 and Take Call. Then click the Respond Immediately check box.Respond Immediately

Save this file as Lesson 1 – Solution 4. Then simulate the model.


The average cycle time for Difficult calls is no 53.95 minutes. Remember management wanted that time to be under 60 minutes.


13. Several alternatives were tried in this lesson. Given your knowledge of business, which solution do you think makes the most sense?
14. What other solutions would you suggest? Do you see how ProcessModel can help you determine the best alternative?
15. Go back to the original call center model. Review the operating parameters and requirements outlined at the beginning of this lesson. Double click each object in the model to locate each of those parameters

Continue with Lesson 2: Replications and Distributions