Practical experience requirements: Facility rating.
CFR · 2024-01-01 · US · Title 14
Each applicant for a facility rating at any air traffic control tower must have satisfactorily served— (a) As an air traffic control tower operator at that control tower without a facility rating for at least 6 months; or (b) As an air traffic control tower operator with a facility rating at a different control tower for at least 6 months before the date he applies for the rating.
official document · source cfr-2024 · id 14:§ 65.39