Customers push their shopping carts to the check- out register where a clerk processes the sale. The market has four registers, but they are not dedicated to specific sales clerks because the clerks play many rolls in the day- to-day operations. In addition to checking out custo- mers, sales clerks will stock shelves, unload delivery trucks, or perform other tasks as demand in various areas rises and falls throughout the day. This fluid work demand makes the assignment of clerks to specific registers impractical.