We have 4 identical units (and just ordered another one). When one started acting up (giving false positives etc) we sent it for calibration. The process was easy and now the unit performs perfectly. Our units are used hard every day and this service keeps them accurate.
I returned it to be recalibrated because it stopped giving me readings. Total time for shipping and recalibration was less than estimated and the unit works fine again. Worth the money.
The calibration service is awesome. Easy to fill forms, easy payment, fast service and within no time is back. you don't need to worry. You can trust the service.