The ECTS grade transfer scale is an interface grade scale to help European universities, students and employers to understand the level of student achievement. Hence, the ECTS scale can be seen as an interface, transforming local scales to a common system where A-E denote passing grades. By definition, ECTS should distribute the passing students into five cohorts representing fixed percentiles. This paper presents a generic method to distribute cohorts of students with differentiated passing local grades into ECTS, or any other grading scale, cohorts. It takes into account historic student performance, the percentiles required for the scale in question as well as the relative performance of a student group in relation to student groups previously graded in the same course module. This method can handle any number of equally or unequally spaced local grade cohorts of any size, and it allows direct transfer between local grades in the spirit of ECTS. (Contains 3 figures and 6 tables.)