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The plasma panel is a 2-level type of display possessing local memory, high luminance, and selective write-erase capability. There are, however, no convenient inexpensive methods for interacting graphically with material displayed on a panel by means of a hand-held stylus. A simple and potentially low-cost technique has been developed in which a light pen can be used to point at any part, dark or light, of a plasma panel, thus making an economical interactive plasma-display system possible. The technique is based on the ability to selectively address one cell of the panel with a sequence of two interrogating pulses. Therefore, depending on the state of the addressed cell, one or the other interrogating pulse will cause the addressed cell to flash at a time different from all other cells, without altering the state of the addressed cell or disturbing the unselected cells. The light pen is gated to look for these light pulses and their individual Phase in order to establish the location of the light pen and the state of the cell. The operating margins for the interrogating pulses exceed the panel's own write-erase margins, and the additional hardware required beyond the normal panel sustain and select circuitry is negligible.