Abstract: A head mounted display system is shown having a single optical element. The single optical element has three optical surfaces. An entrance surface receives a video image directly from a display. A reflective surface reflects the video image from the entrance surface to an exit surface wherein the user views the video image directly through the exit surface. The three optical surfaces are shaped to generate a virtual image that is magnified, appears at a distance from the user and substantially free from distortion, astigmatism and chromatic aberrations. The optical element is adjustably mounted on a frame of the head up display system to accommodate users with different interpupillary distances and to vary the apparent distance between the user and virtual image.

Abstract: The conical tip of a load applying member (42) acts against one side (136) of a movable plate (120). A spring (84) urges the conical tip of a biasing member (88) against the other side (138). In response to a relatively small movement of member (42) against plate (120), plate (120) pivots about a first axis a.sub.1 to depress the operator (102) of a first snap-action switch (98). In response to a relatively large movement of member (42), plate (120) pivots away from contact with operator (102), first about auxiliary axis a.sub.4 and then about third axis a.sub.3. In response to an intermediate movement, plate (120) pivots to depress the operator (103) of a second snap-action switch (99), first about second axis a.sub.2 and then about auxiliary axis a.sub.4. Axis a.sub.4 is defined by first and second fulcrums (71, 134). Axis a.sub.2 is defined by second fulcrum (134 ) and operator (102); axis a.sub.3 is defined by first fulcrum (71) and operator (103). Axis a.sub.