In all of the applications we have seen so far, a user is indirectly aware of the actions of another through telepointers, encoding of users by colours, audio feedback, and other features. Clearboard [], designed for two-user collaboration, shows that it is possible for a user to be directly aware of the actions of a remote use. It appears to each user that other user is behind a transparent whiteboard, and the drawings made by the two users are shared rather than overlaid. Thus, one user can, for instance, erase a drawing made by another user or refine it. .
Mirrors, projectors, and a multiuser shared whiteboard application are used to create this illusion of face-to-face awareness. The displays of the users are tilted 45 degrees, and the image of a user is is reflected by a mirror, captured by an overhead camera, and transmitted to a rear projector at the other site which overlays the image on the screen. The shared whiteboard application ensures that users share changes to the objects drawn on the whiteboard.