Thermco's ACCU-SAFE - Enclosed Chamber Thermometers are precise, reliable and an economical means of measuring critical temperatures in Blood Bank Refrigerators, Ultra-Low Freezers, Freezers, Refrigerators, Incubators, Ambient/Room, Block Heaters and Ovens. All thermometers have their own unique serial number and is supplied with a NIST (National Institute of Standards and Technology) certificate to indicate the traceability of each thermometer and the standard used in the certification testing. ACCU-SAFE Environmentally Friendly Thermometers are Spirit-Filled (Non-Mercury). Mercury model also available. Each thermometer is encapsulated in a flouropolymer safety-shield which absorbs shock, and will enclose the liquid and splintered glass within the coating should breakage occur. Thereby keeping contaminants from user and environment.