NIST stands for National Institute of Standards and Technology. Infrared thermometers with this certification mean that they passed the said agency’s standards in terms of accuracy. To get this NIST certificate, the product has to be tested by a third-party official tester which means that the manufacturer who wants this certificate has to pay an extra fee for the testing. NIST certified IRs are essential for research and hospital use. However, if it is just for residential use, there is no need to buy those expensive models with NIST certification.