CDC recommends that you use only a temperature monitoring device (TMD) with a Certificate of Calibration Testing (also known as a Report of Calibration). This certificate provides the TMD’s level of accuracy compared to a recognized standard. This certificate comes with the TMD when it is purchased, and it is different than the manufacturer’s warranty. While all TMDs are calibrated during manufacturing, certified calibrated TMDs undergo a second individual calibration against a reference standard from an accredited testing laboratory. Calibration testing should be done every 2 to 3 years or according to the manufacturer’s suggested timeline to ensure the accuracy of the device continues to conform to nationally accepted standards. Additional information on this topic is available on page 11 of CDC’s Vaccine Storage and Handling Toolkit, available at www.cdc.gov/vaccines/hcp/admin/storage/toolkit/storage-handling-toolkit.pdf.