When an LWIR sensor is calibrated, the question generally arises as to what the precision, accuracy, and repeatability are for the calibration. The measurement precision is the formulation and interpretation of the terms "accuracy" and "repeatability." A derivation is presented in this paper in which a logical formulation of these terms is obtained. Forms for both short-term and long-term uncertainties are given. In addition, the use of confidence intervals in connection with sensor calibration is discussed, along with an appropriate example. A compilation of uncertainty terms and the definitions of these terms are proposed for adoption by the LWIR community.