Abstract: A spark plug is held by a work holder, and an illumination device is disposed between a rear end surface of a metal terminal of the spark plug and a lens of a CCD camera. The positional relationship among the rear end surface, the lens and a light source is determined such that regular reflected light resulting from regular reflection of irradiation light emitted from the light source and impinging on the rear end surface is not incident on the lens. In capturing an image of the rear end surface not only is the regular reflected light not incident on the lens, but also the incidence, on the lens of irregular reflected light resulting from irregularities on the rear end surface is reduced, whereby interference of reflected light with a captured image can be reduced.

Abstract: A spark plug is held by a work holder, and an illumination device is disposed between a rear end surface of a metal terminal of the spark plug and a lens of a CCD camera. The positional relationship among the rear end surface, the lens and a light source is determined such that regular reflected light resulting from regular reflection of irradiation light emitted from the light source and impinging on the rear end surface is not incident on the lens. In capturing an image of the rear end surface not only is the regular reflected light not incident on the lens, but also the incidence, on the lens of irregular reflected light resulting from irregularities on the rear end surface is reduced, whereby interference of reflected light with a captured image can be reduced.

Abstract: Data, including letters, numerals and marks, are sequentially scrolled on a display. When a switch is pushed, the scroll is interrupted, and then the data being displayed is fixed. An arrangement may be made such that the scroll occurs at a high speed first and then occurs at a low speec in response to the operation of the switch. Further, the data being displayed may be caused to blink for a confirmation purpose.