It’s recommended to re-calibrate the Prisma DI different models once every 3 years. A calibration certificate valid for 3 years will be provided upon carrying out the re-calibration service by PrismaTibro here in Sweden. To return your Prisma DI instrument to us for general check-up and re-calibration, please submit your request and we will respond by providing our service reference and address. If you cannot book the freight by your own to return your Prisma DI back to us, then please let us know to help you. We are collaborating with DHL who can collect your Prisma DI and return it to us, while you will be charged for the freight cost.