This paper addresses the issue of transmission error (TE) evaluation. The motivation for writing this paper is the research on TE measurement and calculation, which focuses on finding a correlation between TE and the noise performance of spur gears. In the context of the study a research of an accurate description of the procedure for evaluating the TE waveform was carried out, but only incomplete descriptions were found. Therefore, the author tries to describe this problema according to the available sources and his own experience. The beginning of this article includes a description of what transmission error is and how it can be determined. The main part of this article, however, concerns developing a method for evaluating transmission error and introducing some new ideas on how to evaluate this magnitude more accurately.