In some cases, pursuant to a definite plan for the permanent reduction of the normal scheduled workweek from say, 48 hours to 40 hours, an agreement is entered into with a view to lessening the shock caused by the expected reduction in take-home wages. The agreement may provide for a rising scale of rates as the workweek is gradually reduced. The varying rates established by such agreement will be recognized as bona fide in the weeks in which they are respectively operative provided that (a) the plan is bona fide and there is no effort made to evade the overtime requirements of the Act; (b) there is a clear downward trend in the duration of the workweek throughout the period of the plan even though fluctuations from week-to-week may not be constantly downward; and (c) the various rates are operative for substantial periods under the plan and do not vary from week-to-week in accordance with the number of hours which any particular employee or group happens to work.