Clock Setup Tutorial

There are several things to setup on your Clock to ensure you get the most from your simulation. The clock is integral to Discrete Event Simulation because it tells you the time in your model.

Before going any further you need to decide which time units to work in (seconds/minutes/hours). You should also think about how long to run your simulation for (i.e. do you want to look at your process over a day/week/month/year?).

To access your Clock Properties at any time, simply double click on the clock, or right click and select ‘Clock Properties’. You can also access Clock Properties through the Data & Rules tab.

The first thing to decide is whether you want a digital or analog clock. This can be setup by choosing ‘Digital’ or ‘Clock Face’ on the Clock Properties screen.

You also have the option of adding the Week and Date to your clock by selecting or deselecting ‘Day,Week’ and ‘Date’.

Displaying Weeks on the Clock

On models with a shorter Results Collection Period, displaying the Week is less relevant; however when you start modelling a year at a time, it can be a quick way of seeing how far through a year your simulation is.

Duration of a Day

Under the ‘Running Time’ section of Clock Properties, you can set up the duration of a business day. This requires the Start Time and the Duration of the day (not the end time).

Simul8’s default is to run for a 40 hour week (9am - 5pm Monday - Friday). For example, a 9am - 5pm day would look like this:

If your process runs for 24 hours per day, you should set Running time as below.


There are also options to include an extension of Overtime in the simulation day. Check the box for “Extend with Overtime”, and then enter the maximum time to be added to the clock at the end of the day to help process items in the system. Arrivals will cease during overtime to allow other objects to process work after hours. The maximum time entered is in the format of the current time units for the simulation.

The below screenshot offers an example of a simulation day running from 9am-5pm, but will continue processing work for an additional 60 minutes until 6pm to try and clear the system.

Time Units

The next thing to set up is the type of Time Unit you want to use within your simulation. All timing values in your simulation will follow this time unit. For example, if you choose ‘Hours’, all values must be entered in hours.

For this reason, minutes is the most common time unit used in Simul8. It is much easier to enter a large number of minutes to equal a couple of hours (e.g. 240 minutes = 4 hours) than it is to work in hours and try to work out what 23 minutes (for example) equates to.

Set up your time units here:

Note that when changing the time unit, this will apply to all existing Objects. Therefore, an Activity’s Timing set to 10 minutes, will be set to 10 hours, if hours as selected as a Time unit.

Results Collection Period

By default, your simulation will run for 1 week. If you want to run for a different amount of time, you need to adjust your Results Collection Period.

There is a Results Collection Period button on the Clock Properties window; this displays the following dialog.

You can choose whether you want to run for 1 day, 10 years, or somewhere in between.

Warm Up Period

The Warm Up Period is the time at the start of your run, where your simulation has not got up to maximum productivity yet. For example, a machine can be switched on at the start of a day at 9am, but it is ready to process items after 30 minutes after it has been switched on.

In some simulations, you may not want to include your warm up period in your results; in this case you should enter a Warm Up Period so that your simulation doesn’t start collecting results until after this specified time.

The Warm Up Period button is also located on Clock Properties. The following dialog will ask you what Warm Up Period you would like to enter.

Applying Working hours to specific parts of the Simulation

If the Start Time and the Duration are not the same for all Objects in your Simulation, you can either use:

  • Shifts : When you want to define what times of day parts of your simulation work;
  • Calendars : When you want to control more complex patterns of working days, such as deciding specific time periods that an Activity does or doesn’t operate.

Timing for each step in your process

The next step is to include timing information for each step in your process. Click on Activity 1; the Activity Properties should appear on the toolbar at the top of your screen.

In the ‘Average’ box, you can see that the time to process each items in this Activity is set to a default value of 10 minutes. Change this to 5 minutes by clicking in the ‘Average’ box.

You can also change the name of the Activity using the ‘Name’ box on the far left of the toolbar. Alter the name to ‘Process 1’ – the Activity properties box should now look like the picture above.

In reality, events don’t always occur at fixed times - for instance, patients don’t arrive 5 exactly 5 minutes apart to a doctor’s surgery. In order to account for this randomness, Simul8 uses Distributions to build in real life variability. The Distribution in your simulation is currently set to Average. This means that the time Process1 takes to complete work on each work item will vary. You can change the distribution used by selecting the dropdown menu.

Next change the processing times of the other Activities to 5 minutes each.

In order to edit the timing of arrivals within your process, click on the Start Point and change the Average Arrival Timing to 5 in the top toolbar.

The Start Point uses the Inter Arrival Time, or time between each item arriving. This means that roughly once every 5 minutes an item is pushed into the simulation (this equates to 12 items per hour).

If the Inter Arrival Time is shorter, more items will enter the simulation over the same time period. Now, experiment with different distributions. You will have seen queues building up – what happens if you change the Processing times and Inter Arrival Time to fixed Distributions?

See Also