Metre Convention
Many measuring devices need to be recalibrated at regular intervals. These devices might be petrol pumps. They might be weighing scales. They might be complex medical equipment like MRI scanners. A certificate is issued when the device is recalibrated. The device that is used to do the calibration must itself be calibrated. These devices are often recalibrated in a national metrology laboratory. Legal problems can arise if a calibration done in one country is not recognised in another country.