Medical devices glassware one-time calibration What does it mean?

According to my understanding, a one-time calibration of measuring instruments are non-critical measuring instruments, because it only needs to be calibrated for the first time, do not need to trace the value on a regular basis, on the contrary, critical measuring instruments must be periodically calibrated, which the definition of calibration and verification must be understood clearly. Such as calibration of the cycle requirements are not very strict, only need to analyze the calibrated data and correct the deviation, to ensure that the accuracy of the value of the use of the period, the verification of the cycle is required, generally not allowed to exceed the validity of the inspection, the special mandatory inspection of measuring instruments, inspection of the validity of the period must not be exceeded.