All test equipment should be calibrated to ensure correct operation and accurate results. Equipment calibration is a good example of the old addage ‘rubbish in equals rubbish out’, tests are meaningless unless you can be confident they are at the correct levels. This confidence can only be built on evidence that all elements of your equipment are performing within defined specifications. Everything from sensors to measurement hardware should be calibrated on a regular basis, thought it is down to you the user to determine a period that suits your quality management system. Even accessories should be checked albeit not necessarily calibrated, consider cables, are you sure they have no intermittent signal issues?