Evaluation of translation quality is a central issue in translation pedagogy. The use of the error marking scale developed by the American Translators Association for the grading of certification exams is discussed as a way to introduce professional standards of error marking into the translator training classroom. The problems of adapting a product-oriented and testing-oriented scale for process-oriented classroom evaluation are explored, as well as the technical details of mathematically adapting the scale to an A-F grading system. An Excel spreadsheet is used to calculate grades and adjust for length of text.