<hardware> An early pointing device which the user pointed at a raster-scanned display screen. A photocell in the pen detected the flying spot of the raster scan. The position of the spot at that instant, obtained from the scanning electronics, was made available to software as (x, y) co-ordinates.
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Nearby terms: light client « light-emitting diode « light-emitting resistor « light pen » light pipe » light-weight » Lightweight Directory Access Protocol