Thermocouple, fold-out thermometer that has extreme accuracy to +/-0.2° when measuring -30°C to 150°C, remaining ranges are +/-0.5°C accurate. The 4.25" probe is waterproof (IP65), which makes it idealfor high humidity areas. C/F° switchable. Resolution is 0.1°C with a 4 second response time in water. 511-3601 comes with an NIST Traceable Certificate. The 511-3602 comes with an NIST Certificate of Accuracy, which the customer chooses one temperature for certification.