Applicants with specialized experience can have that experience credited towards meeting the basic requirements for professional occupations that permit qualification on the basis of experience as well as education. Such experience may be creditable not only for meeting the basic requirements, but also for positions at GS-7 and above if it is comparable to that which would have been gained in a two-grade interval professional series and clearly demonstrates that the applicant has the necessary background to perform satisfactorily the duties of the position to be filled.