Each thermometer features a black liquid and yellow back glass which creates a distinct contrast making this thermometer very easy to read. These thermometers are also individually calibrated to NIST standards at specific temperature and supplied with an NIST report of calibration stating corrections to one-tenth the smallest division. All Enviro-Safe glass thermometers contain an environmentally friendly non-mercury liquid that is 100% certified as non-toxic, non-hazardous, and fully biodegradable. In case of breakage the liquid can be cleaned up easily with soap and water. These thermometers come complete with ring top anti-roll fitting, individual serial number, NIST report of calibration, recyclable packaging, and are RoHS compliant.