Indication: The value given by a measuring instrument or measuring system.

Indication error: The difference between the indication of a measuring instrument and the reference value of the corresponding input quantity.

Maximum allowable measurement error (maximum allowable error): The limit of measurement error relative to a known reference value allowed by a specification or procedure for a given measurement, measuring instrument or measuring system.

Correction: Compensation for estimated systematic errors.

Accuracy grade: The grade or level of a measuring instrument or measuring system that, under specified working conditions, meets specified metrological requirements and keeps measurement errors or instrumental uncertainties within specified limits.