The type of employment agreement permitted under section 7(f) can be made only with (or by his representatives on behalf of) an employee whose “duties * * * necessitate irregular hours of work.” It is clear that no contract made with an employee who works a regularly scheduled workweek or whose schedule involves alternating fixed workweeks will qualify under this subsection. Even if an employee does in fact work a variable workweek, the question must still be asked whether his duties necessitate irregular hours of work. The subsection is not designed to apply in a situation where the hours of work vary from week to week at the discretion of the employer or the employee, nor to a situation where the employee works an irregular number of hours according to a predetermined schedule. The nature of the employee's duties must be such that neither he nor his employer can either control or anticipate with any degree of certainty the number of hours he must work from week to week. Furthermore, for the reasons set forth in § 778.406, his duties must necessitate significant variations in weekly hours of work both below and above the statutory weekly limit on nonovertime hours. Some examples of the types of employees whose duties may necessitate irregular hours of work would be outside buyers, on-call servicemen, insurance adjusters, newspaper reporters and photographers, propmen, script girls and others engaged in similar work in the motion picture industry, firefighters, troubleshooters and the like. There are some employees in these groups whose hours of work are conditioned by factors beyond the control of their employer or themselves. However, the mere fact that an employee is engaged in one of the jobs just listed, for example, does not mean that his duties necessitate irregular hours. It is always a question of fact whether the particular employee's duties do or do not necessitate irregular hours. Many employees not listed here may qualify. Although office employees would not ordinarily qualify, some office employees whose duties compel them to work variable hours could also be in this category. For example, the confidential secretary of a top executive whose hours of work are irregular and unpredictable might also be compelled by the nature of her duties to work variable and unpredictable hours. This would not ordinarily be true of a stenographer or file clerk, nor would an employee who only rarely or in emergencies is called upon to work outside a regular schedule qualify for this exemption.