Let us focus just on what is mandatory in ISO 9001:2015. Calibration is mandatory just for those resources that are used to decide if the final product/service is according to specifications. So, go back to your organization’s outputs, the applications, and check if there is any specification that needs to be tested with some monitoring and measurement resource. Let me speculate. If your organization’s application gives GPS coordinates with some stated degree of error, for professional services, perhaps you should calibrate that. If your organization’s application gives temperature readings or measures light intensity, or moisture level… as important attributes, then perhaps calibration should be needed. Other examples of calibration needs can be around biometrics as facial recognition and fingerprint reading in order to be aware of performan ce and error levels. And perhaps tests with different hardware to set the borders as a function of hardware used and your applications. Since we are entering a “Star Trek” world, with more and more use of non-invasive ways to diagnose situations. This will be the future.