You are not the only one wondering. Many customers ask this question and we will gladly provide you with more information. There are various reasons; however, all of them reflect the necessity:
Legal or company-specific regulations, such as quality and energy management, stipulate regular calibration.
The accuracy of any measurement deteriorates over the operating history due to temperature or pressure variations, shock and vibrations or mechanical loss.
Safety-relevant as well as environmental aspects can be taken into account through measures of calibration.