Abstract: The invention relates to an instrument adapted for difficult conditions of use, such as a diver's computer or the like, said instrument comprising a computer (2) as well as displaying device (6) for displaying to a user at least the control and/or output information related to said computer (2). The display (7) of said displaying device (6) is arranged in a casing (1) in such a manner that said display (7) can be clearly read from two essentially different directions (A and B). A first side of a structurally transparent display (7) is read directly (direction A) from the top of said display (7), and the opposite side is read essentially from the opposite side (direction B) of said casing through a special optical assembly (12) so that a mirror image is read of an image observed from the back side of said display (7).