(a) The application must set forth the facts relied upon to show that the established basic rate is substantially equivalent to the average hourly earnings of the employee exclusive of overtime premiums over a representative period of time. 21 The basic rate will be considered “substantially equivalent” to the average hourly earnings of the employee if, during a representative period, the employee's total overtime earnings calculated at the basic rate in accordance with the applicable overtime provisions are approximately equal to the employee's total overtime earnings computed on his average hourly earnings for each workweek in accordance with section 7(a) of the Act. 22

(b) The length of time constituting a representative period will depend on the factors that cause the employee's average hourly earnings to vary appreciably from week to week. For instance, if the variation in earnings of an employee paid on an incentive basis is due to the difference in availability of work in the slow and busy seasons the period used for comparison of overtime earnings would have to include both a slow and a busy season in order to be representative. Likewise, if a piece-worker's average hourly earnings vary appreciably from week to week because of differences in materials or styles worked on, the period used for purposes of comparison would have to include work on the different materials and styles in order to be representative.