Although, as stated in the preceding section, two or more departments of a business may constitute a single establishment, two or more physically separated portions of a business though located on the same premises, and even under the same roof in some circumstances may constitute more than one establishment for purposes of exemptions. In order to effect such a result physical separation is a prerequisite. In addition, the physically separated portions of the business also must be engaged in operations which are functionally separated from each other. Since there is no such functional separation between activities of selling goods or services at retail, the Act recognizes that food service activities of such retail or service establishments as drugstores, department stores, and bowling alleys are not performed by a separate establishment which “is” a “restaurant” so as to qualify for the overtime exemption provided in section 13(b)(8) and accordingly provides a separate overtime exemption in section 13(b)(18) for employees employed by any “retail or service establishments” in such activities in order to equalize the application of the Act between restaurant establishments and retail or service establishments of other kinds which frequently compete with them for customers and labor. (See Sen. Rept. 1487, 89th Cong. first session, p. 32.) For retailing and other functionally unrelated activities performed on the same premises to be considered as performed in separate establishments, a distinct physical place of business engaged in each category of activities must be identifiable. The retail portion of the business must be distinct and separate from and unrelated to that portion of the business devoted to other activities. For example, a firm may engage in selling groceries at retail and at the same place of business be engaged in an unrelated activity, such as the incubation of chicks for sale to growers. The retail grocery portion of the business could be considered as a separate establishment for purposes of the exemption, if it is physically segregated from the hatchery and has separate employees and separate records. In other words, the retail portion of an establishment would be considered a separate establishment from the unrelated portion for the purpose of the exemption if (a) It is physically separated from the other activities; and (b) it is functionally operated as a separate unit having separate records, and separate bookkeeping; and (c) there is no interchange of employees between the units. The requirement that there be no interchange of employees between the units does not mean that an employee of one unit may not occasionally, when circumstances require it, render some help in the other units or that one employee of one unit may not be transferred to work in the other unit. The requirement has reference to the indiscriminate use of the employee in both units without regard to the segregated functions of such units.