An exclusive observation station shall follow a self-decided calibration cycle of each equipped observation instrument and apply for an instrument calibration from a Calibration Unit to prove it be qualified for use, and then can be used.The error of an observation instrument is within the tolerant error as listed in the attached “Criteria for accreditation of the observation instruments” shall be considered as qualified.（see attached tables） The difference between the displayed value of the observation instrument under calibration and the standard value of the standard device is named the error of that observation instrument; the tolerant errors settled for each type of observation instruments are named the maximum permissible errors.