Time Dependant Workload (Part 2 of 2)
Back to our example, if we decide to round the number, the result of the above hour would be two. You do this math for every hour you are open and you end up with figure 1 below. If you lay out your workload through time, you’ll see the number of employees varying during the day. It directly reflects your customer’s flow.
Figure 1. Number of employees required per time of day
Some of you may say that since employees have a different productivity (some cashiers are faster than others for example), you could schedule according to the customer output directly. Why translate to number of employees, right? This would be the optimal way to schedule since you could have your fastest cashier on staff and therefore need one less cash register open, which would save you money. Then why isn’t it done this way? Simply to keep things manageable. Otherwise, a planner would need to measure against all sorts of different drivers to establish a schedule and it would become quite a challenge to manage. Imagine your fastest cashier calling in sick: does this mean you replace that person with two other cashiers? The daily management of the schedule would quickly become overwhelming. So be practical and express your workload in number of employees required.
The cashier workload is now ready. You’ll notice that in our example, there are some big peaks and valleys. The number of customers would require up to ten registers for one hour. In our store, not only we do not even have ten registers, but we can’t ask folks to come in for only one hour of work. There will be constraints (see chapter 4) that impose a minimum duration when someone is scheduled to work.
Again, to help yourself and for simplicity, you can smooth out the employee requirements by reducing the peaks that represent noise. The more your resolution gets to be precise, the more of these peaks you will see. The same goes for valleys where all of the sudden no cash register is required because you don’t expect customers between 9am and 10am let’s say. You’ll still need a minimum of one cashier open no matter what the customer count is. So in your translation exercise, put a minimum and a maximum. Also, look at differentials between the previous hour and the next hour. For example, if you need 2 cashier for one hour, then 10 cashiers for the next hour, then again 3 cashiers for the next two hours, you can see that this 10 should be 3 or 4 but will not be 10. Rule of thumb: when you have peaks like this, you may have the ability to schedule shifts that overlap (the end of the shift overlaps by one hour the beginning of the next one). Therefore, you can make this workload at the previous hour (2) added to the next hour (3) and make that number a 5 instead of a 10.
The same logic applies to valleys, but in this case, you may elect to keep the valleys intact and not readjust according to the previous and next hours. These valleys will allow you to schedule breaks later in the process or dispatch the time independent workload.
This daily workload not only will be different on each weekday, but will also change from week to week as seasonal patterns will influence customer behavior. Holiday season will have higher traffic than the beginning of the year when no special events are happening. Total volume will therefore change from week to week.