Let’s take the Cashier workload and analyze how we will quantify that one. This workload has only time dependant tasks and therefore is directly related to the number of customers showing up at the cash register. These customers will have different number of items to buy and will pay through different methods (cash, credit, check, etc). As explained earlier, each customer will take some time to check out and each cashier will have a limited capacity in number of customers.
The first thing to do is to pick a resolution and a unit of measure. The unit of measure is the time it takes to serve a customer. The resolution is the period of time where you will measure the count of customers. You can count the number of customers per 15 minutes or per hour or anywhere below, above, or in between. Usually, you choose a resolution that is manageable depending on the tools you have. If you have a pen and paper, I would suggest never going lower than one hour. If you use Excel, you could manage all the way down to 30 minutes. High end software allow for as low as 5 minutes in some cases.
You may wonder why would anyone manage a schedule down to the 5-minute increment? In our simplified example of one store, the amount of time to service a customer will be counted in minutes. No point in counting seconds because I have four cash registers which of only two are open most of the time. So if I say it takes 55 seconds to serve a customer and I round it up to one minute to keep my math simple, the difference on the week is insignificant. Take 5 seconds times the number of customers visits, say two thousand, makes 10,000 seconds a week, which is roughly 3 hours over the whole schedule. Not much. By padding the time required to serve a customer, you are adding hours to your workload quantity that is not necessarily required but that saves you aggravation and funny math.
But if our grocery store is successful and if we buy more stores and now have a chain of hundreds of store, you can multiply that 3 hours by 200 stores which makes 600 hours of extra time scheduled. Use any hourly amount, it starts to become significant. And if you perform the same exercise for all tasks, your over-scheduled number becomes very significant. This is why large enterprises do buy software that measure to the second the tasks that are performed in order to reduce the waste that accumulates due to rounding. Your workload definitions will therefore get longer and more detailed and will be measured more precisely as you grow your business. It will be directly proportional. If you don’t, you are exposed to over scheduling once you get to the schedule.
So for the sake of simplicity in our example, we will pick a one minute per customer average serving time and a one-hour resolution. Therefore if it takes one minute to serve one customer, our cashier has a capacity of 60 customers per hour. We take the expected business of that hour (say we expect 100 customers), this would create 100 minutes of work to do in one hour. You divide the amount of work by the resolution (100/60) and you get 1.66 employees. Since you can’t schedule two thirds of a person, you have to decide what to do with the fraction (do you schedule someone or not). You may elect to cut the fraction all the time, make the fraction whole all the time (if the result is 1.1, make it 2) or simply round the result. This will have a direct impact on service and cost. If you decide to cut the fraction all the time, it’s good for cost, but bad for service. If you decide to make the fraction whole all the time, it’s good for service but bad for profit. You could also decide to have a different rule depending on the relative part of the fraction. In the math above 0.66 out of 1.66 is a big proportion. You could have a requirement for 10.66 employees. In this case, deciding between 10 or 11 employees will have a much reduced impact on customer service because the capacity is not greatly affected (versus choosing between 1 or 2 employees which represents 50% reduction in capacity). You can already feel that even though you haven’t even started talking about employees, a simple rule of thumb decided by a planner may have a huge impact on the business’s success.