WORKSHEET 1 (THE DRILL)

A one machine shop processes two job types on a single drill. A job type 1 arrives every 10 minutes and requires 4 minutes to process on the drill. Type 2 jobs begin arriving at time 3 and continue to arrive every 6 minutes thereafter. Each type 2 job requires 3 minutes to process on the drill.

Determine the number of jobs of each type which are processed in one 8 hour shift.

Blocks to include in the Model

ASSIGN, CREATE, COUNT, DELAY, DISPOSE, QUEUE, RELEASE, SEIZE.

Elements to include in the Experiment

ATTRIBUTES, COUNTERS, QUEUES, REPLICATE, RESOURCES.

Additional Work

Modify the experiment frame to enable you to :

1. View the working of the model with the interactive debugger.

2. View the working of the model using the trace command.

Results

Your model should give the following results :

Number of type 1 jobs = 48

Number of type 2 jobs = 80

## 8.9 Collecting Statistics

We have already used the `COUNT' block for collecting data from the model but, of course, we need to collect a much wider range of information from a typical model. The `TALLY' and `DSTAT' elements are able to help us with this.

`TALLY' records a single observation and stores it in a file as an entity passes the `TALLY' element. You can record any ARENA variable, attribute or combination of variables and attributes defined by an equation.

### Example 8.3

You may tally the total length of pipe passing the tally element when an entity representing a lorry loaded with `num_pipes' passes using the element :

We have assumed that the Tally ID is Total_pipes and that `pipe_length' is an ARENA variable and num_pipes is an attribute of the Entity lorry.

Perhaps the most common use of this element is to record the time interval between an entity passing some point in the model and reaching the `TALLY' block. You achieve this by using the `MARK' feature which allows you to mark an attribute with the current simulation time TNOW as an entity passes a block. You can use this `MARK' feature with any block. At the `TALLY' block you then have to use the special function:

INTERVAL (attribute_ID) which can be shortened to INT(attribute_ID)

This will allow the `TALLY' block to record the simulation time interval which has passed since the entity was `marked' with TNOW.