Precise Measurement Yellow or White Back Celsius or Fahrenheit Scale Certified at Multiple Points Individually Serialized For accurate temperature measurements. Use to calibrate or check accuracy of routine thermometers. Thermometer 61222-552 is spirit-filled against white back glass. Certified Easy-Read thermometers 61018-148, -152, and -150 feature nonhazardous, nontoxic, biodegradable black Enviro-Safe liquid against yellow back glass. Certified Enviro-Safe thermometer 43300-294 features green Enviro-Safe liquid against white back glass. Other thermometers are mercury-filled against yellow back glass. All thermometers are individually calibrated and certified against National Institute of Standards and Technology Traceable equipment. A certificate is provided outlining the traceability, tests, and results. Thermometer 61054-682 is manufactured at the National Institute of Standards and Technology laboratory. A certificate bearing the seal of the institute is provided outlining individual tests and results.