Like any other analytical instrument, breathalyzers need routine calibration to ensure their accuracy. Calibration compensates for aging of sensor and other critical components. We strongly recommend that you calibrate your breathalyzer once every year or sooner. Our Calibration Procedures? Perform functional test Test and calibrate the unit for its entire reading range Use automated DOT approved "Wet Bath Simulators" Replace mouthpieces Replace exterior plastic parts if broken Complete the task in 5 working days How Do I Send My Unit In for Calibration? Purchase your calibration coupon for each unit Send the unit in its original packaging, if possible Please DO NOT SEND any mouthpieces nor batteries Write calibration coupon number on the shipping label Describe any or all problems in details. Make sure to mail the unit insured or at least with a delivery confirmation ticket Include a calibration coupon with your gift