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Operator-Cashier Analogy


For years, industrial engineers have dealt with issues of balancing manufacturing production. What is the most cost-effective amount of production capacity given variable demand for the products? You donít want idle equipment, but you also donít want to lose sales by not having enough product.

Consider this case - Imagine that you manage a retail store. Early on the rate of customers arriving to check out is less than the rate at which the cashier can check them out. There is no line, and the cashier has some spare time. As the store gets busy, the rate of customers to check out exceeds the cashierís check out rate and a line/queue forms.

  • Eventually fewer customers arrive, and the line disappears. If the line gets too long, some shoppers will leave without buying. If they are purchasing one low price item, you are only mildly concerned, but it really isnít worth adding another cashier.
  • However, you donít want to lose a shopper buying a large number of high priced items. You could add cashiers so that no queue ever formed. You could add cashiers to prevent the line from getting so long that anyone left, ensuring that customers with big ticket items donít leave along with the dollar general crowd.
  • Cost/Benefit analysis might indicate that the cost of losing some of the low-dollar customers is less than adding cashiers, certainly less than adding cashiers so there is never a queue. Or, if you could identify the high dollar folks, having a special lane or opening a special register would cost less than adding a full time cashier.

Now, make some small changes to the situation. Make the customers job-related tasks and the price of the items their priority (required speed of response * consequence of inaction). The cashier is the operator. A customer leaving is a task not attended to in time for successful action to be taken on it. There is no problem as long as the length of the queue does not result in losing customers (tasks).

It still might be okay for a short time to lose the low dollar (low priority tasks) customers as long as it doesnít also cause a loss of the high dollar (high priority tasks) customers. The goal in staffing is to match the right personnel, with the right skills, to the required work, at the right time.

Whatís the point? Refinery managers are often faced with the critical question -- How many people are needed to safely and efficiently operate a process unit?

First, steady-state demands of a unit may exceed the minimum 24/7 staffing required to secure a unit. In such a case, a day operator position (ďspecial registerĒ) may be utilized to serve as a focal point for administrative and maintenance tasks. Second, it might be okay to have periods of times when a queue of tasks develops, as long as they can all be handled within their required time period. Third, it might also be okay to have short times when some tasks are not completed, as long as they are of low importance.

For further information, visit the links below.

| Alarm & Display System Analysis Overview | Alarm Management | Display Design | Alarm & Display Design Seminar | Beville Shape Calculator -Excel download | Alarm Distribution Estimator -Excel download |


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