The faceplate of a square-planar picture tube is relatively flat, with a curvature along the major axis and lines parallel thereto that is generally greater near the left and right edges than in the center. An LC tuned circuit, coupled to the deflection winding, has a resonant period of oscillation approximately half that of the line trace interval. The tuned circuit introduces an oscillatory correction component into the trace current that provides additional S-shaping in that portion of the line scan intermediate the center and the left or right edge.
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