A contrast adjustment system (100) for a display device of a watch (10), the case (12) of which can be removably arranged in an enclosure (4) of a thermal protection housing (1) for mechanical and/or functional components (5) of the watch (10), the display device being arranged facing a crystal (6) of the housing (1), the housing (1) including a reversible fastening device (13) fastening the case (12) of a watch (10) in the enclosure (4) while keeping it away from functional elements (15) of this housing (1), the elements (15) forming this enclosure (4) including a middle (9a), a back (9b) and the crystal (6) of this housing (1), the system (100) including an electronic device (110) configured to adjust the contrast of the display device when the electronic device (110) and the housing (1) are connected to each other.