Range is an interactive whiteboard designed to support collocated, ad-hoc meetings. It employs proximity sensing to proactively transition between ambient and authoring modes, clear space for writing, and cluster ink strokes. The inspiration for Range stems from longitudinal studies of student design teams, in which we observed that shifts in collaborative activity correlated with changes in the users' physical proximity to the whiteboard. Through iterative design, we developed techniques for incorporating implicit input like that of the proximity sensors into interaction. Keywords Implicit interaction, proxemics, ambient, proactive, whiteboard, CSCW ACM Classification Keywords H5.2. Information interfaces and presentation: User Interfaces-input devices and strategies, interaction styles.