In general as the manufacturer or calibration laboratory we cannot give you a clear specification for the recalibration interval of a measuring instrument. The change of a measuring instrument depends on the instrument itself, the way of use, the environment and of course on your precision requirements. Usually we recommend to start with a recalibration interval of 12 months (or less in case of extremely stressed usage). With the second calibration you are already able to make a statement about the stability of the measuring instrument and if an increase of the recalibration interval to 24 months is possible. Of course a accidental defect or damage is always possible. So the maximum assigned recalibration interval after years is thought to be more a question of the entrepreneurial risk.