Abstract
Gianfranco Spavieri, George T. Gillies & Espen Gaarder Haug (The Sagnac effect and the role of simultaneity in relativity theory, Journal of Modern Optics (2021)), claim that the Sagnac effect reveals the theory of relativity is incorrect and inconsistent. We prove that when standard relativity is appropriately interpreted, it is observationally correct and logically sound.