An apparatus including a crystal or a screen wherein the crystal or the screen is arranged to ensure sealing and an anti-scratch protection of said apparatus which is intended to display an information visible to a user through the crystal or the screen, said apparatus including: - a first material layer made of an unbreakable transparent plastic polymer, the first material layer being arranged on said apparatus so that a first face is arranged on the information side and a second face on the user side, the first material layer being fastened on the apparatus in a tight manner, - a second material layer made of a transparent glass having an anti-scratch surface, in particular a sapphire glass, superimposed on the first layer and constituting the outer portion of the crystal or the screen of the apparatus, the second layer having an outer face arranged on the user side and an inner face arranged on the information side, and in which the second material layer made of a transparent glass includes, carried by its inner face, a transparent repositionable glue film, this repositionable glue film ensuring the repositionable adherence of the second material layer on the first material layer, whereas the second material layer with its repositionable glue film can be removed so as to be able to be replaced by another second material layer provided with a transparent repositionable glue film, without breaking the sealing of said apparatus ensured by the first material layer which remains permanently fastened on said apparatus, The apparatus also including positioning means for facilitating the positioning of the second material layer on the first material layer, said positioning means including a protrusion or a groove, arranged on the outer or inner periphery of the first material so that these positioning means surround all or part of the second material layer which covers the first material layer. - a first material layer made of an unbreakable transparent plastic polymer, the first material layer being arranged on said apparatus so that a first face is arranged on the information side and a second face on the user side, the first material layer being fastened on the apparatus in a tight manner, - a second material layer made of a transparent glass having an anti-scratch surface, in particular a sapphire glass, superimposed on the first layer and constituting the outer portion of the crystal or the screen of the apparatus, the second layer having an outer face arranged on the user side and an inner face arranged on the information side, and in which the second material layer made of a transparent glass includes, carried by its inner face, a transparent repositionable glue film, this repositionable glue film ensuring the repositionable adherence of the second material layer on the first material layer, whereas the second material layer with its repositionable glue film can be removed so as to be able to be replaced by another second material layer provided with a transparent repositionable glue film, without breaking the sealing of said apparatus ensured by the first material layer which remains permanently fastened on said apparatus, The apparatus also including positioning means for facilitating the positioning of the second material layer on the first material layer, said positioning means including a protrusion or a groove, arranged on the outer or inner periphery of the first material so that these positioning means surround all or part of the second material layer which covers the first material layer.