This paper presents general formulation, mathematical methods and numerical examples of least squares adjustment (reconciliation) of the results of the measurement of thermal energy processes. This paper contains results of research of two groups supervised by Professors T. Styrylska and Z. Kolenda. Almost all problems discussed in the paper were suggested by Professor Jan Szargut a mentor and tutor of the authors. The methods presented have been successfully applied in mathematical modeling in both a global and local sense. A list of selected publications is collected in the references. (C) 2018 Elsevier Ltd. All rights reserved.