A display apparatus includes a display module for displaying an image, and a variable member for varying a shape of the display module. The device, when deployed, generates expansions ahead of compressions generated by off-design conditions, inlet spillage for example, and enables maintenance of a low boom signature. In another form of the invention, the identical base portion of the decorative member can be interconnected with the support base by means of a threaded rod which is threadably received within a threaded bore formed in the base portion of the decorative member. By detecting the variation of the magnetic field, the movement and thus the target angular velocity can be measured.