| 摘要 |
In a method of measuring a focus of a cathode ray tube, a predetermined image is displayed at a predetermined position on the screen of the cathode-ray tube. A focussing voltage of the cathode ray tube is changed under a condition that a distance from a reference position to a predetermined position in the image is detected. A change state of the detected distance is displayed on a display. Further, an image having representation of at least a vertical-direction line and a horizontal-direction line is employed as the predetermined image. A line sensor is located so as to cross both of the vertical-direction line and the horizontal-direction line to set a predetermined position of the line sensor as the reference position. A change of a first distance from the reference position to an edge of the vertical-direction line within the image read by the line sensor and a change of a second distance from the reference position to an edge of the horizontal-direction line within the image read by the line sensor are detected. The detected changes of the respective distances are displayed on orthogonal coordinates.
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