In 2002, Japanese Industrial standard JIS Z 2340 has issued to provide the instruction of new methodology to calibrate the observing conditions of surface testing such as liquid penetrant and magnetic particle testing applying visual calibration gauges. The visual calibration gauges are the transparent plates, on which the line pairs printed to be used to confirm the resolution of visual testing observing view. The concept of line pair has been used to evaluate the resolutions of optical instruments, and the line pair value is a numerical value that shows how many line pairs can be distinguished as separate lines within 1 millimeter. In this paper, the background of the development and the general outlines of visual calibration gauges are introduced at first. And then applications of the gauges and detail process to calibrate the surface testing observing view conditions are also described.