The first level of detail is commonly called a physical data flow diagram. Figure 3-12 is an example for our payroll illustration. A physical DFD closely resembles the document flowcharts discussed earlier in this chapter; that is, it focuses on physical entities such as the employees involved in the system under study, as well as the tangible documents, reports, and similar hard-copy inputs and outputs that flow through the system. Thus, for example, the bubbles in the physical DFD of Figure 3-12 identify the data-entry clerk who enters payroll information into the computer, the payroll cashier who distributes paychecks to employees, and the tax accountant who sends tax information to the Internal Revenue Service of the federal government.